Signaling for decoder-side intra mode derivation

ABSTRACT

Example implementations include a method and of video processing, comprising determining, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit. The implementations further include performing the conversion based on the determining.

BACKGROUND

The present disclosure relates generally to video coding, and more particularly, to video encoding and decoding based on signaling for decoder-side intra-prediction mode derivation (DIMD).

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

An example implementation includes a method of video decoding, comprising determining to apply DIMD to a decoding unit of an encoded bitstream. The method further comprising performing a conversion between a video comprising a plurality of pictures and a bitstream of the video, wherein DIMD is applied to the unit using an intra prediction mode (IPM) based on the determining.

The disclosure also provides a device including a memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to perform the above method, a device including means for performing the above method, and a non-transitory computer-readable medium storing computer-executable instructions for performing the above method.

Another example implementation includes a method of video decoding, comprising determining to apply DIMD to a unit of a bitstream. The method further comprising performing a conversion between a video comprising a plurality of pictures and a bitstream of the video, wherein DIMD and an intra coding tool are applied to the unit using an intra prediction mode (IPM) based on the determining.

The disclosure also provides a device including a memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to perform the above method, a device including means for performing the above method, and a non-transitory computer-readable medium storing computer-executable instructions for performing the above method.

Another example implementation includes a method of video decoding, comprising determining to apply DIMD to a unit of a bitstream. The method further comprising performing a conversion between a video comprising a plurality of pictures and a bitstream of the video, wherein information related to DIMD is signalled within the bitstream as a syntax element based upon the unit.

The disclosure also provides a device including a memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to perform the above method, a device including means for performing the above method, and a non-transitory computer-readable medium storing computer-executable instructions for performing the above method.

Another example implementation includes a method of video decoding, comprising determining to apply DIMD to a unit of a bitstream. The method further comprising performing a conversion between a video comprising a plurality of pictures and a bitstream of the video, wherein DIMD and an intra coding tool are applied to the unit using an intra prediction mode (IPM) based on the determining.

The disclosure also provides a device including a memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to perform the above method, a device including means for performing the above method, and a non-transitory computer-readable medium storing computer-executable instructions for performing the above method.

The disclosure also provides a device including a memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to perform the above method, a device including means for performing the above method, and a non-transitory computer-readable medium storing computer-executable instructions for performing the above method.

To the accomplishment of the foregoing and related ends, the one or more aspects include the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail some illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates an example of a video coding system, in accordance with some aspects of the present disclosure.

FIG. 2 is a block diagram that illustrates a first example of a video encoder, in accordance with some aspects of the present disclosure.

FIG. 3 is a block diagram that illustrates an example of a video decoder, in accordance with some aspects of the present disclosure.

FIG. 4 is a block diagram that illustrates a second example of a video encoder, in accordance with some aspects of the present disclosure.

FIG. 5 is an example of an encoder block diagram of versatile video coding (VVC) in accordance with some aspects of the present disclosure.

FIG. 6 is a schematic diagram of intra mode coding with 67 intra-prediction modes to capture the arbitrary edge directions presented in natural video in accordance with some aspects of the present disclosure.

FIGS. 7 and 8 are reference example diagrams of wide-angular intra-prediction in accordance with some aspects of the present disclosure.

FIG. 9 is a diagram of discontinuity in case of directions that exceed 45° angle in accordance with some aspects of the present disclosure.

FIG. 10 is a schematic diagram of location of the samples used for the derivation of α and β for the chroma in accordance with some aspects of the present disclosure.

FIG. 11 is a schematic diagram of location of the samples used for the derivation of α and β for the luma in accordance with some aspects of the present disclosure.

FIGS. 12-15 illustrate examples of reference samples (Rx,−1 and R−1,y) for PDPC applied over various prediction modes in accordance with some aspects of the present disclosure.

FIG. 16 is a diagram of multiple reference line (MRL) intra-prediction used in accordance with aspects of the present disclosure.

FIGS. 17 and 18 are example diagrams and of an intra sub-partitions (ISP) that divides luma intra-predicted blocks vertically or horizontally into sub-partitions depending on the block size in accordance with some aspects of the present disclosure.

FIG. 19 is a diagram of a matrix weighted intra-prediction process (MIP) method for VVC in accordance with some aspects of the present disclosure.

FIG. 20 is a diagram of a template based intra mode derivation where the target denotes the current block (of block size N) for which intra-prediction mode is to be estimated in accordance with some aspects of the present disclosure.

FIG. 21 is a diagram of a template of a set of chosen pixels on which a gradient analysis may be performed based on intra-prediction mode derivation in accordance with some aspects of the present disclosure.

FIG. 22 is a diagram of a convolution of a 3×3 sobel gradient filter with the template in accordance with aspects of the present disclosure.

FIG. 23 is a schematic diagram of intra mode coding with greater than 67 intra-prediction modes to capture the arbitrary edge directions presented in natural video in accordance with some aspects of the present disclosure.

FIG. 24 is a diagram of an example template including a left-above sub-template in accordance with some aspects of the present disclosure.

FIG. 25 is a diagram of an example template including a left sub-template and an above sub-template in accordance with some aspects of the present disclosure.

FIG. 26 is a diagram of an example template including an above sub-template in accordance with some aspects of the present disclosure.

FIG. 27 is a diagram of an example template including a left sub-template in accordance with some aspects of the present disclosure.

FIG. 28 is a diagram of an example template including a left sub-template and a left-below sub-template in accordance with some aspects of the present disclosure.

FIG. 29 is a diagram of an example template including an above sub-template and a right-above sub-template in accordance with some aspects of the present disclosure.

FIG. 30 is a diagram of an example template including a left sub-template, a left-below sub-template, an above sub-template, and a right-above sub-template in accordance with some aspects of the present disclosure.

FIG. 31 is a diagram of an example template including a left-above sub-template, a left sub-template, a left-below sub-template, an above sub-template, and a right-above sub-template in accordance with some aspects of the present disclosure.

FIG. 32 is a diagram of an example template including sub-templates that are spaced apart from a target block in accordance with some aspects of the present disclosure.

FIG. 33 is a diagram of example template-reference samples for a template including a left-above sub-template, a left sub-template, and an above sub-template in accordance with some aspects of the present disclosure.

FIG. 34 is a diagram of example template-reference samples for a template including a left sub-template and an above sub-template in accordance with some aspects of the present disclosure.

FIG. 35 is a diagram of example template-reference samples for a template including an above sub-template in accordance with some aspects of the present disclosure.

FIG. 36 is a diagram of example template-reference samples for a template including a left sub-template in accordance with some aspects of the present disclosure.

FIG. 37 is a diagram of example template-reference samples with a horizontal gap for a template including an above sub-template in accordance with some aspects of the present disclosure.

FIG. 38 is a diagram of example template-reference samples with a vertical gap for a template including an above sub-template in accordance with some aspects of the present disclosure.

FIG. 39 is a diagram of example template-reference samples with a vertically shifted portion for a template in accordance with some aspects of the present disclosure.

FIG. 40 is a diagram of example template-reference samples with a horizontally shifted portion for a template in accordance with some aspects of the present disclosure.

FIG. 41 is a diagram of a first example computing device in accordance with some aspects of the present disclosure.

FIG. 42 is a diagram of a second example computing device in accordance with some aspects of the present disclosure

FIG. 43 is a flowchart of a first example method of video processing in accordance with some aspects of the present disclosure.

FIG. 44 is a flowchart of a second example method of video processing in accordance with some aspects of the present disclosure.

FIG. 45 is a flowchart of a third example method of video processing in accordance with some aspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to a person having ordinary skill in the art that these concepts may be practiced without these specific details. In some instances, structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of video coding and decoding will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, among other examples (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, among other examples, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more examples, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

The present aspects generally relate to the signaling of DIMD in video coding. As described in detail herein, video coding technologies, such as high efficiency video coding (HEVC), versatile video coding (VVC), etc., can use IPMs at the encoder and decoder to encode/decode each image or frame of a video, such to compress the number of bits in the bitstream, which can provide for efficient storage or transmission of the image or frame, and thus the video. As described in further detail herein, the IPMs are determined or specified per block of an image, where a block can include a portion of the image defined by a subset of coding units CUs or prediction units (PUs) (e.g., N×N CUs or PUs), where each CU or PU can be a pixel, a chroma, a luma, a collection of such, etc. The IPM is then used to predict a given block based on reference pixels, chromas, lumas, of a previously decoded block. As such, use of IPMS may no longer require storing or communicating particular values for each pixel, chroma, or luma, etc.

In current video coding technologies, an IPM used for encoding a block may be signalled in the bitstream, which may require significant overhead. In accordance with aspects described herein, the IPM used for intra-prediction may be derived at the decoder via DIMD. Deriving the IPM may reduce the bitrate of the bitstream by reducing the bits used for signaling the IPM. For example, intra mode information (e.g., the IPM) may be derived at both encoder and decoder from the neighbouring reconstructed samples of current block (i.e., previously decoded blocks). The present disclosure relates to enhancements to DIMD, and in particular, incorporating DIMD into video coding technologies that leverage other intra coding tools. For instance, in some instances, an intra coding tool may not support use of IPMs, and/or a video decoder may not be able to determine when to perform DIMD and/or how to perform DIMD when a video coder also employs other intra coding tools.

FIG. 1 is a block diagram that illustrates an example of a video coding system 100 that may utilize the techniques of this disclosure. As shown in FIG. 1 , video coding system 100 may include a source device 110 and a destination device 120. The source device 110, which may be referred to as a video encoding device, may generate encoded video data. The destination device 120, which may be referred to as a video decoding device, may decode the encoded video data generated by the source device 110. The source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.

The video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures or images. The terms “picture,” “image,” or “frame” can be used interchangeably throughout to refer to a single image in a stream of images that produce a video. The video encoder 114 encodes the video data from the video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. The I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter, a bus, or substantially any mechanism that facilitates transfer of data between devices or within a computing device that may include both the source device 110 and destination device 120 (e.g., where the computing device stores the encoded video generated using functions of the source device 110 for display using functions of the destination device 120). In one example, the encoded video data may be transmitted directly to destination device 120 via the I/O interface 116 through the network 130 a. The encoded video data may also be stored onto a storage medium/server 130 b for access by destination device 120.

The destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122. The I/O interface 126 may include a receiver and/or a modem, a bus, or substantially any mechanism that facilitates transfer of data between devices or within a computing device. The I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130 b. The video decoder 124 may decode the encoded video data. The display device 122 may display the decoded video data to a user. The display device 122 may be integrated with the destination device 120, or may be external to the destination device 120 which be configured to interface with an external display device.

The video encoder 114 and the video decoder 124 may operate according to a video compression standard, such as the HEVC standard, VVC standard and other current and/or further standards.

FIG. 2 is a block diagram illustrating an example of a video encoder 200, which may be an example of the video encoder 114 in the system 100 illustrated in FIG. 1 , in accordance with some aspects of the present disclosure.

The video encoder 200 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 2 , the video encoder 200 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video encoder 200. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure, including those of video encoder 200.

The functional components of video encoder 200 may include one or more of a partition unit 201, a prediction unit 202 which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205 and an intra-prediction unit 206, a residual generation unit 207, a transform unit 208, a quantization unit 209, an inverse quantization unit 210, an inverse transform unit 211, a reconstruction unit 212, a buffer 213, and an entropy encoding unit 214.

In other examples, the video encoder 200 may include more, fewer, or different functional components. In an example, the prediction unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform prediction in an IBC mode in which at least one reference picture is a picture where the current video block is located.

Furthermore, some components, such as the motion estimation unit 204 and the motion compensation unit 205, may be highly integrated, but are separately represented in the example of FIG. 2 for purposes of explanation.

The partition unit 201 may partition a picture into one or more video blocks. The video encoder 200 and the video decoder 300 may support various video block sizes.

The mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to at least one of a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some examples, the mode select unit 203 may select a combination of intra- and inter-prediction (CIIP) mode in which the prediction is based on an inter-prediction signal and an intra-prediction signal. The mode select unit 203 may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter-prediction.

To perform inter-prediction on a current video block, the motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. In an example, each reference frame can correspond to a picture of the video. The motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from the buffer 213 other than the picture associated with the current video block.

The motion estimation unit 204 and the motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I-slice, a P-slice, or a B-slice. As used herein, in some aspects, an “I-slice” may refer to a portion of a picture composed of macroblocks, all of which are based upon macroblocks within the same picture. Further, as used herein, in some aspects, “P-slices” and “B-slices” may refer to portions of a picture composed of macroblocks that are not dependent on macroblocks in the same picture.

In some examples, the motion estimation unit 204 may perform uni-directional prediction for the current video block, and the motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. The motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. The motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. The motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.

In other examples, the motion estimation unit 204 may perform bi-directional prediction for the current video block, where the motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. The motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. The motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. The motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.

In some examples, the motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.

In some examples, the motion estimation unit 204 may not output a full set of motion information for the current video. Rather, the motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, the motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

In one example, the motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as the another video block.

In another example, the motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signaling techniques that may be implemented by video encoder 200 include advanced motion vector prediction (AMVP) and merge mode signaling.

The intra-prediction unit 206 may perform intra-prediction on the current video block. When the intra-prediction unit 206 performs intra-prediction on the current video block, the intra-prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include at least one of a predicted video block or one or more syntax elements.

The residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.

In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and the residual generation unit 207 may not perform the subtracting operation.

The transform unit 208, which may also be referred to as a transform processing unit, may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.

After the transform unit 208 generates a transform coefficient video block associated with the current video block, the quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

The inverse quantization unit 210 and the inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. The reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the prediction unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.

After the reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed to reduce video blocking artifacts in the video block.

The entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.

FIG. 3 is a block diagram illustrating an example of video decoder 300, which may be an example of the video decoder 124 in the system 100 illustrated in FIG. 1 , in accordance with some aspects of the present disclosure.

The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 3 , the video decoder 300 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video decoder 300. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure, including those of video decoder 300.

In the example of FIG. 3 , the video decoder 300 includes one or more of an entropy decoding unit 301, a motion compensation unit 302, an intra-prediction unit 303, an inverse quantization unit 304, an inverse transformation unit 305, a reconstruction unit 306, and a buffer 307. The video decoder 300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200 (FIG. 2 ).

The video decoder 300 may receive, via the entropy decoding unit 301 or otherwise, an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). In this example, the entropy decoding unit 301 may decode the entropy coded video data. Based on the decoded video data, whether entropy decoded or otherwise, the motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. The motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode. AMVP may be used, including derivation of several most probable candidates based on data from adjacent PBs and the reference picture. Motion information typically includes the horizontal and vertical motion vector displacement values, one or two reference picture indices, and, in the case of prediction regions in B slices, an identification of which reference picture list is associated with each index. As used herein, in some aspects, a “merge mode” may refer to deriving the motion information from spatially or temporally neighboring blocks.

The motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in syntax elements received with the encoded bitstream or in separate assistance information, e.g., as specified by a video encoder when encoding the video.

The motion compensation unit 302 may use interpolation filters as used by video encoder 200 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. The motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.

The motion compensation unit 302 may use some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence. As used herein, in some aspects, a “slice” may refer to a data structure that can be decoded independently from other slices of the same picture, in terms of entropy coding, signal prediction, and residual signal reconstruction. A slice can either be an entire picture or a region of a picture.

The intra-prediction unit 303 may use intra-prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Intra-prediction can be referred to herein as “intra,” and/or intra-prediction modes can be referred to herein as “intra modes” The inverse quantization unit 304 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transform unit 305 applies an inverse transform.

The reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 302 or intra-prediction unit 303 to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in buffer 307, which provides reference blocks for subsequent motion compensation/intra-prediction and also produces decoded video for presentation on a display device.

Although the following description may be focused on High Efficiency Video Coding (HEVC), and/or the standard Versatile Video Coding (VVC), the concepts described herein may be applicable to other coding standards or video codec.

FIG. 4 shows an example of a block diagram of a HEVC video encoder and decoder 400, which may be the video encoder 114 and video decoder 124 in the system 100 illustrated in FIG. 1 , video encoder 200 in FIG. 2 and video decoder 300 in FIG. 3 , etc., in accordance with some aspects of the present disclosure. The encoding algorithm for generating HEVC-compliant bitstreams may proceed as follows. Each picture can be divided into block regions (e.g., coding tree units (CTUs)), and the precise block division may be transmitted to the decoder. A CTU consists of a luma coding tree block (CTB) and the corresponding chroma CTBs and syntax elements. The size L×L of a luma CTB can be chosen as L=16, 32, or 64 samples, where the larger sizes can enable higher compression. HEVC then supports a partitioning of the CTBs into smaller blocks using a tree structure and quadtree-like signaling. The quadtree syntax of the CTU specifies the size and positions of its luma and chroma CBs. The root of the quadtree is associated with the CTU. Hence, the size of the luma CTB is the largest supported size for a luma CB. The splitting of a CTU into luma and chroma CBs may be jointly signalled. One luma CB and ordinarily two chroma CBs, together with associated syntax, form a coding unit (CU). A CTB may contain only one CU or may be split to form multiple CUs, and each CU has an associated partitioning into prediction units (PUs) and a tree of transform units (TUs).

The first picture of the video sequence (and/or the first picture at each clean random access point that enters the video sequence) can use only intra-picture prediction, which uses region-to-region spatial data prediction within the same picture, but does not rely on other pictures to encode the first picture. For the remaining pictures between sequential or random access points, the inter-picture temporal prediction coding mode may be used for most blocks. The encoding process for inter-picture prediction includes selecting motion data including a selected reference picture and a motion vector (MV) to be applied to predict samples of each block.

The decision whether to code a picture area using inter-picture or intra-picture prediction can be made at the CU level. A PU partitioning structure has its root at the CU level. Depending on the basic prediction-type decision, the luma and chroma CBs can then be further split in size and predicted from luma and chroma prediction blocks (PBs). HEVC supports variable PB sizes from 64×64 down to 4×4 samples. The prediction residual is coded using block transforms. A TU tree structure has its root at the CU level. The luma CB residual may be identical to the luma transform block (TB) or may be further split into smaller luma TBs. The same applies to the chroma TBs.

The encoder and decoder may apply motion compensation (MC) by using MV and mode decision data to generate the same inter-picture prediction signal, which is transmitted as auxiliary information. The residual signal of intra-picture or inter-picture prediction can be transformed by linear spatial transformation, which is the difference between the original block and its prediction. Then the transform coefficients can be scaled, quantized, entropy encoded, and transmitted together with the prediction information.

The encoder can duplicate the decoder processing loop so that both can generate the same prediction for subsequent data. Therefore, the quantized transform coefficients can be constructed by inverse scaling, and then can be inversely transformed to replicate the decoding approximation of the residual signal. The residual can then be added to the prediction, and the result of this addition can then be fed into one or two loop filters to smooth the artifacts caused by block-by-block processing and quantization. The final picture representation (i.e., the copy output by the decoder) can be stored in the decoded picture buffer for prediction of subsequent pictures. In general, the order of encoding or decoding processing of pictures may be different from the order in which they arrive from the source. As such, in some examples, it may be necessary to distinguish between the decoding order of the decoder (that is, the bit stream order) and the output order (that is, the display order).

Video material encoded by HEVC can be input as a progressive image (e.g., because the source video originates from this format or is generated by de-interlacing before encoding). There is no explicit coding feature in the HEVC design to support the use of interlaced scanning, because interlaced scanning is no longer used for displays and becomes very uncommon for distribution. However, metadata syntax has been provided in HEVC to allow the encoder to indicate that it has been sent by encoding each area of the interlaced video (i.e., even or odd lines of each video frame) into a separate picture interlaced video, or by encoding each interlaced frame as a HEVC encoded picture to indicate that it has been sent. This can provide an effective method for encoding interlaced video without the need to support special decoding processes for it.

FIG. 5 is an example of an encoder block diagram 500 of VVC, which can include multiple in-loop filtering blocks: e.g., deblocking filter (DF), sample adaptive offset (SAO) adaptive loop filter (ALF), etc. Unlike DF, which uses predefined filters, SAO and ALF may utilize the original samples of the current picture to reduce the mean square errors between the original samples and the reconstructed samples by adding an offset and by applying a finite impulse response (FIR) filter, respectively, with coded side information signaling the offsets and filter coefficients. ALF may be located at the last processing stage of each picture and can be regarded as a tool to catch and fix artifacts created by the previous stages.

FIG. 6 is a schematic diagram 600 of intra-prediction mode coding with 67 intra-prediction modes to capture the arbitrary edge directions presented in natural video. In some examples, the number of directional intra modes may be extended from 33, as used in HEVC, to 65 while the planar and the DC modes remain the same.

In some examples, the denser directional intra-prediction modes may apply for the block sizes and for both luma and chroma intra-predictions. In the HEVC, every intra-prediction mode coded block may include a square shape (e.g., a coded block of size N×N) and the length of each of its side may be a power of 2 (e.g., where Nis a power of 2). Thus, no division operations are required to generate an intra-predictor using DC mode. In VVC, blocks can have a rectangular shape that may necessitate the use of a division operation per block in the general case. To avoid division operations for DC prediction, the longer side may be used to compute the average for non-square blocks.

Although 67 modes are defined in the VVC, the exact prediction direction for a given intra-prediction mode index may be further dependent on the block shape. Conventional angular intra-prediction directions are defined from 45 degrees to −135 degrees in clockwise direction. In VVC, several conventional angular intra-prediction modes may be adaptively replaced with wide-angle intra-prediction modes for non-square blocks. The replaced modes may be signalled using the original mode indexes, which are remapped to the indexes of wide angular modes after parsing. In some examples, the total number of intra-prediction modes may be unchanged, i.e., 67, and the intra mode coding method may also be unchanged.

FIGS. 7 and 8 are reference example diagrams 700 and 800 of wide-angular intra-prediction. In some examples, the number of replaced modes in wide-angular direction mode may depend on the aspect ratio of a block. The replaced intra-prediction modes are illustrated in Table 1:

TABLE 1 Intra-prediction modes replaced by wide-angular modes Aspect ratio Replaced intra-prediction modes W/H == 16 Modes 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 W/H == 8 Modes 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 W/H == 4 Modes 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 W/H == 2 Modes 2, 3, 4, 5, 6, 7, 8, 9 W/H == 1 None W/H == ½ Modes 59, 60, 61, 62, 63, 64, 65, 66 W/H == ¼ Mode 57, 58, 59, 60, 61, 62, 63, 64, 65, 66 W/H == ⅛ Modes 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66 W/H == 1/16 Modes 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66

FIG. 9 is a diagram 900 of discontinuity in case of directions that exceed 45° angle. In such instance, two vertically adjacent predicted samples may use two non-adjacent reference samples in the case of wide-angle intra-prediction. Hence, low-pass reference samples filter and side smoothing may be applied to the wide-angle prediction to reduce the negative effect of the increased gap Apa. If a wide-angle mode represents a non-fractional offset, there may be 8 modes in the wide-angle modes satisfy this condition, which are [−14, −12, −10, −6, 72, 76, 78, 80]. When a block is predicted by these modes, the samples in the reference buffer can be directly copied without applying any interpolation. With this modification, the number of samples to be smoothed may be reduced.

In VVC, 4:2:2 and 4:4:4 chroma formats are supported as well as 4:2:0. Chroma derived mode (DM) derivation table for 4:2:2 chroma format was initially ported from HEVC extending the number of entries from 35 to 67 to align with the extension of intra-prediction modes. As HEVC specification does not support prediction angle below −135 degree and above 45 degree, luma intra-prediction modes ranging from 2 to 5 may be mapped to 2. Therefore, chroma DM derivation table for 4:2:2: chroma format can be updated by replacing some values of the entries of the mapping table to convert prediction angle more precisely for chroma blocks.

In some aspects, for each inter-predicted CU, motion parameters consisting of motion vectors, reference picture indices and reference picture list usage index, and additional information used for the new coding feature of VVC may be used for inter-predicted sample generation. The motion parameter can be signalled in an explicit or implicit manner. When a CU is coded with skip mode, the CU may be associated with one PU and may have no significant residual coefficients, no coded motion vector delta or reference picture index. A merge mode may be specified where the motion parameters for the current CU can be obtained from neighboring CUs, including spatial and temporal candidates, and additional schedules introduced in VVC. The merge mode can be applied to any inter-predicted CU, not only for skip mode. The alternative to merge mode may be the explicit transmission of motion parameters, where motion vector, corresponding reference picture index for each reference picture list and reference picture list usage flag and other needed information are signalled explicitly per each CU.

Additionally or alternatively, intra block copy (IBC) may be a tool adopted in HEVC extensions on SCC, and thus may be used by a video encoder 114, 200, 400, as described herein in encoding video, and/or by a video decoder 124, 300, 400, as described herein in decoding video. Such a tool may improve the coding efficiency of screen content materials. As IBC mode may be implemented as a block level coding mode, block matching (BM) may be performed at the encoder to find the optimal block vector (or motion vector) for each CU. Here, a block vector is used to indicate the displacement from the current block to a reference block, which is already reconstructed inside the current picture. The luma block vector of an IBC-coded CU may be in integer precision. The chroma block vector can round to integer precision as well. When combined with AMVR, the IBC mode can switch between 1-pel and 4-pel motion vector precisions. An IBC-coded CU may be treated as the third prediction mode other than intra- or inter-prediction modes. The IBC mode may be applicable to the CUs with both width and height smaller than or equal to 64 luma samples.

At the encoder side, hash-based motion estimation may be performed for IBC. The encoder performs RD check for blocks with either width or height no larger than 16 luma samples. For non-merge mode, the block vector search may be performed using hash-based search first. If hash search does not return valid candidate, block matching based local search may be performed. In the hash-based search, hash key matching (32-bit cyclic redundancy check (CRC)) between the current block and a reference block may be extended to all allowed block sizes. The hash key calculation for every position in the current picture may be based on 4×4 sub-blocks. For the current block of a larger size, a hash key may be determined to match that of the reference block when all the hash keys of all 4×4 sub-blocks match the hash keys in the corresponding reference locations. If hash keys of multiple reference blocks are found to match that of the current block, the block vector costs of each matched reference may be calculated and the one with the minimum cost may be selected.

In some examples, in block matching search, the search range may be set to cover both the previous and current CTUs. At CU level, IBC mode may be signalled with a flag and it can be signalled as IBC AMVP mode or IBC skip/merge mode. In one example, such as IBC skip/merge mode, a merge candidate index may be used to indicate which of the block vectors in the list from neighboring candidate IBC coded blocks is used to predict the current block. The merge list may include spatial, HMVP, and pairwise candidates.

In another example, such as IBC AMVP mode, a block vector difference may be coded in the same way as a motion vector difference. The block vector prediction method uses two candidates as predictors, one from left neighbor and one from above neighbor (if IBC coded). When either neighbor is not available, a default block vector can be used as a predictor. A flag can be signalled to indicate the block vector predictor index.

To reduce the cross-component redundancy, a cross-component linear model (CCLM) prediction mode may be used in the VVC, for which the chroma samples are predicted based on the reconstructed luma samples of the same CU by using a linear model as follows: pred_(C)(i,j)=α·rec_(L)′(i,j)+β   Equation 1

In such instance, pred_(C)(i, j) may represent the predicted chroma samples in a CU and rec_(L)(i, j) may represent the down-sampled reconstructed luma samples of the same CU. The CCLM parameters (α and β) may be derived with at most four neighboring chroma samples and their corresponding down-sampled luma samples. For instance, suppose the current chroma block dimensions are W×H, then W″ and H′ are set as W′=W, H′=H when LM mode is applied; W′=W+H when LM−T mode is applied; and H′=H+W when LM−L mode is applied.

The above neighboring positions may be denoted as S[0, −1] . . . S[W′−1, −1] and the left neighboring positions may be denoted as S[−1, 0] . . . S[−1, H′−1]. Then the four samples are selected as S[W′/4, −1], S[3*W′/4, −1], S[−1, H′/4], S[−1, 3*H′/4] when LM mode is applied and both above and left neighboring samples are available; S[W′/8, −1], S[3*W′/8, −1], S[5*W′/8, −1], S[7*W′/8, −1] when LM−T mode is applied or only the above neighboring samples are available; and S[−1, H′/8], S[−1, 3*H′/8], S[−1, 5*H′/8], S[−1, 7*H′/8] when LM−L mode is applied or only the left neighboring samples are available.

In some aspects, the four neighboring luma samples at the selected positions may be down-sampled and compared four times to find two larger values: x⁰ _(A) and x¹ _(A), and two smaller values: x⁰ _(B) and x¹ _(B). Their corresponding chroma sample values may be denoted as y⁰ _(A), y⁰ _(B) and y¹ _(B). Then x_(A), x_(B), y_(A) and y_(B) may be derived as: X _(a)=(x ⁰ _(A) +x ¹ _(A)+1)>>1;X _(b)=(x ⁰ _(B) +x ¹ _(B)+1)>>1;Y _(a)=(y ⁰ _(A) +y ¹ _(B)+1)>>1;Y _(b)=(y ⁰ _(B) +y ¹ _(B)+1)>>1   Equation 2

Finally, the linear model parameters α and β may be obtained according to the following equations:

$\begin{matrix} {\alpha = \frac{Y_{a} - Y_{b}}{X_{a} - X_{b}}} & {{Equation}\mspace{14mu} 3} \\ {\beta = {Y_{b} - {\alpha \cdot X_{b}}}} & {{Equation}\mspace{14mu} 4} \end{matrix}$

FIG. 10 is a schematic diagram 1000 of location of the samples used for the derivation of α and β for the chroma. FIG. 11 is a schematic diagram 1100 of location of the samples used for the derivation of α and β for the luma. For both FIGS. 10 and 11 , the division operation to calculate parameter a may be implemented with a look-up table. To reduce the memory required for storing the table, the diff value (difference between maximum and minimum values) and the parameter a may be expressed by an exponential notation. For example, the diff value is approximated with a 4-bit significant part and an exponent. Consequently, the table for 1/diff is reduced into 16 elements for 16 values of the significand as follows:

TABLE 2 DivTable [ ] = { 0, 7, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 1, 1, 0 }

In an example, the above template and left template can be used to calculate the linear model coefficients together. In another example, the above template and left template can be used alternatively in the other 2 LM modes, called LM_T, and LM_L modes. In LM_T mode, only the above template may be used to calculate the linear model coefficients. To get more samples, the above template is extended to (W+H) samples. In LM_L mode, only left template is used to calculate the linear model coefficients. To get more samples, the left template may be extended to (H+W) samples. In LM mode, left and above templates are used to calculate the linear model coefficients.

To match the chroma sample locations for 4:2:0 video sequences, two types of down-sampling filter are applied to luma samples to achieve 2 to 1 down-sampling ratio in both horizontal and vertical directions. The selection of down-sampling filter is specified by a SPS level flag. The two down-sampling filters are as follows, which are corresponding to “type-0” and “type-2” content, respectively.

$\begin{matrix} {{{{{Rec}_{L}^{\prime}\left( {i,j} \right)} =}\quad}{\quad{\left\lbrack \begin{matrix} {{{rec}_{L}\left( {{{2i} - 1},{{2j} - 1}} \right)} + {2 \cdot {{rec}_{L}\left( {{{2i} - 1},{{2j} - 1}} \right)}} + {{rec}_{L}\left( {{{2i} + 1},{{2j} - 1}} \right)} +} \\ {{{rec}_{L}\left( {{{2i} - 1},{2j}} \right)} + {2 \cdot {{rec}_{L}\left( {{2i},{2j}} \right)}} + {{rec}_{L}\left( {{{2i} + 1},{2j}} \right)} + 4} \end{matrix} \right\rbrack ⪢ 3}}} & {{Equation}\mspace{14mu} 5} \\ {{{rec}_{L}^{\prime}\left( {i,j} \right)} = {\begin{bmatrix} {{{rec}_{L}\left( {{2i},{{2j} - 1}} \right)} + {{rec}_{L}\left( {{{2i} - 1},{2j}} \right)} + {4 \cdot {{rec}_{L}\left( {{2i},{2j}} \right)}} +} \\ {{{rec}_{L}\left( {{{2i} + 1},{2j}} \right)} + {{rec}_{L}\left( {{2i},{{2j} + 1}} \right)} + 4} \end{bmatrix} ⪢ 3}} & {{Equation}\mspace{14mu} 6} \end{matrix}$

Note that only one luma line (general line buffer in intra-prediction) may be used to make the down-sampled luma samples when the upper reference line is at the CTU boundary. This parameter computation may be performed as part of the decoding process, and not just as an encoder search operation. As a result, no syntax may be used to convey the α and β values to the decoder.

For chroma intra-prediction mode coding, a total of 8 intra-prediction modes are allowed for chroma intra mode coding. Those modes include five traditional intra-prediction modes and three cross-component linear model modes (LM, LM_T, and LM_L). Chroma mode signaling and derivation process are shown in Table 3 below. Chroma mode coding directly depends on the intra-prediction mode of the corresponding luma block. As separate block partitioning structure for luma and chroma components is enabled in I-slices, one chroma block may correspond to multiple luma blocks. Therefore, for Chroma DM mode, the intra-prediction mode of the corresponding luma block covering the center position of the current chroma block can be directly inherited.

TABLE 3 Chroma mode signalling and derivation process Chroma prediction Corresponding luma intra-prediction mode mode 0 50 18 1 X (0 <= X <= 66) 0 66 0 0 0 0 1 50 66 50 50 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X 5 81 81 81 81 81 6 82 82 82 82 82 7 83 83 83 83 83

TABLE 4 Unified binarization table for chroma prediction mode Value of intra_chroma_pred_mode Bin string 4 00 0 0100 1 0101 2 0110 3 0111 5 10 6 110 7 111

In Table 4, the first bin indicates whether it is regular (0) or LM modes (1). If it is LM mode, then the next bin indicates whether it is LM_CHROMA (0) or not (1). If it is not LM_CHROMA, next bin indicates whether it is LM_L (0) or LM_T (1). For this case, when sps_cclm_enabled_flag is 0, the first bin of the binarization table for the corresponding intra chroma_pred_mode can be discarded prior to the entropy coding. In other words, the first bin is inferred to be 0 and hence not coded. This single binarization table is used for both sps_cclm_enabled_flag equal to 0 and 1 cases. The first two bins in Table 4 are context coded with its own context model, and the rest of the bins are bypass coded.

In addition, in order to reduce luma-chroma latency in dual tree, when the 64×64 luma coding tree node is partitioned with Not Split (and ISP is not used for the 64×64 CU) or QT, the chroma CUs in 32×32/32×16 chroma coding tree node is allowed to use CCLM in the following way: If the 32×32 chroma node is not split or partitioned QT split, all chroma CUs in the 32×32 node can use CCLM; Alternatively, if the 32×32 chroma node is partitioned with Horizontal BT, and the 32×16 child node does not split or uses Vertical BT split, all chroma CUs in the 32×16 chroma node can use CCLM. In all the other luma and chroma coding tree split conditions, CCLM is not allowed for chroma CU.

In VVC, the results of intra-prediction of DC, planar and several angular modes may further be modified by a position dependent prediction combination (PDPC) method. PDPC is a prediction method that invokes a combination of the boundary reference samples and HEVC style prediction with filtered boundary reference samples. PDPC can be applied to the following intra modes without signaling: planar, DC, intra angles less than or equal to horizontal, and intra angles greater than or equal to vertical and less than or equal to 80. If the current block is BDPCM mode or MRL index is larger than 0, PDPC is not applied.

The prediction sample pred(x′,y′) is predicted using an intra-prediction mode (DC, planar, angular) and a linear combination of reference samples according to the Equation 7 as follows: pred(x′,y′)=Clip(0,(1<<BitDepth)−1,(wL×R _(−1,y′) +wT×R _(x′,−1)+(64−wL−wT)×pred(x′,y′)+32)>>6)   Equation 7

In the above equation, R_(x,−1), R_(−1,y) may represent the reference samples located at the top and left boundaries of current sample (x, y), respectively

In some aspects, if PDPC is applied to DC, planar, horizontal, and vertical intra modes, additional boundary filters may not be needed, as currently required in the case of HEVC DC mode boundary filter or horizontal/vertical mode edge filters. PDPC process for DC and planar modes is identical. For angular modes, if the current angular mode is HOR_IDX or VER_IDX, left or top reference samples is not used, respectively. The PDPC weights and scale factors are dependent on prediction modes and the block sizes. PDPC is applied to the block with both width and height greater than or equal to 4.

FIGS. 12-15 illustrate examples of reference samples 1200, 1300, 1400, 1500 (R_(x,−1) and R_(−1,y)) for PDPC applied over various prediction modes. The prediction sample pred(x′, y′) is located at (x′, y′) within the prediction block. As an example, the coordinate x of the reference sample R_(x,−1) is given by: x=x′+y′+1, and the coordinate y of the reference sample R_(−1,y) is similarly given by: y=x′+y′+1 for the diagonal modes. For the other angular mode, the reference samples R_(x,−1) and R_(−1,y) could be located in fractional sample position. In this case, the sample value of the nearest integer sample location is used.

FIG. 16 is a diagram 1600 of multiple reference line (MRL) intra-prediction used in accordance with aspects of the present disclosure. In some examples, the samples of segments A and F are not fetched from reconstructed neighboring samples but padded with the closest samples from Segment B and E, respectively. HEVC intra-picture prediction uses the nearest reference line (i.e., reference line 0). In MRL, 2 additional lines (reference line 1 and reference line 3) are used.

In some examples of video coding, the index of selected reference line (mrl_idx) can be signalled and used to generate intra predictor. For reference line index, which is greater than 0, the most probable mode (MPM) list may only include additional reference line modes and the MPM index can be signalled without remaining modes. The reference line index can be signalled before intra-prediction modes, and planar mode can be excluded from intra-prediction modes in case a non-zero reference line index is signalled.

MRL can be disabled for the first line of blocks inside a CTU to prevent using extended reference samples outside the current CTU line. Also, PDPC can be disabled when an additional line is used. For MRL mode, the derivation of DC value in DC intra-prediction mode for non-zero reference line indices can be aligned with that of reference line index 0. MRL may store 3 neighboring luma reference lines with a CTU to generate predictions. The Cross-Component Linear Model (CCLM) tool may store 3 neighboring luma reference lines for its down-sampling filters. The definition of MRL to use the same 3 lines can be aligned as CCLM to reduce the storage requirements for decoders.

FIGS. 17 and 18 are examples of diagrams 1700 and 1800 of an intra sub-partitions (ISP) that divides luma intra-predicted blocks vertically or horizontally into sub-partitions depending on the block size. For example, minimum block size for ISP is 4×8 (or 8×4). If block size is greater than 4×8 (or 8×4) then the corresponding block can be divided by 4 sub-partitions. It has been noted that the M×128 (with M≤64) and 128×N (with N≤64) ISP blocks could generate a potential issue with the 64×64 VDPU. For example, an M×128 CU in the single tree case has an M×128 luma TB and two corresponding M/2×64 chroma TBs. If the CU uses ISP, then the luma TB can be divided into four M×32 TBs (only the horizontal split is possible), each of them smaller than a 64×64 block. However, in the current design of ISP chroma blocks are not divided. Therefore, both chroma components may have a size greater than a 32×32 block. Analogously, a similar situation could be created with a 128×N CU using ISP. Hence, these two cases may be an issue for the 64×64 decoder pipeline. For this reason, the CU sizes that can use ISP may be restricted to a maximum of 64×64. FIGS. 17 and 18 shows examples of the two possibilities. All sub-partitions fulfill the condition of having at least 16 samples.

In ISP, the dependence of 1×N/2×N subblock prediction on the reconstructed values of previously decoded 1×N/2×N subblocks of the coding block is not allowed so that the minimum width of prediction for subblocks becomes four samples. For example, an 8×N (N>4) coding block that is coded using ISP with vertical split is split into two prediction regions each of size 4×N and four transforms of size 2×N. Also, a 4×N coding block that is coded using ISP with vertical split is predicted using the full 4×N block; four transform each of 1×N is used. Although the transform sizes of 1×N and 2×N are allowed, it is asserted that the transform of these blocks in 4×N regions can be performed in parallel. For example, when a 4×N prediction region contains four 1×N transforms, there is no transform in the horizontal direction; the transform in the vertical direction can be performed as a single 4×N transform in the vertical direction. Similarly, when a 4×N prediction region contains two 2×N transform blocks, the transform operation of the two 2×N blocks in each direction (horizontal and vertical) can be conducted in parallel. In this example, there may be no delay, or reduced delay, added in processing these smaller blocks than processing 4×4 regular-coded intra blocks.

TABLE 5 Block Size Coefficient group Size 1 × N, N ≥ 16  1 × 16 N × 1, N ≥ 16 16 × 1  2 × N, N ≥ 8  2 × 8 N × 2, N ≥ 8  8 × 2 All other possible M × N cases 4 × 4

For each sub-partition, reconstructed samples are obtained by adding the residual signal to the prediction signal. Here, a residual signal is generated by the processes such as entropy decoding, inverse quantization and inverse transform. Therefore, the reconstructed sample values of each sub-partition can be available to generate the prediction of the next sub-partition, and each sub-partition is repeatedly processed. In addition, the first sub-partition to be processed is the one containing the top-left sample of the CU and then continuing downwards (horizontal split) or rightwards (vertical split). As a result, reference samples used to generate the sub-partitions prediction signals may only be located at the left and above sides of the lines. All sub-partitions can share the same intra mode. The followings are summary of interaction of ISP with other coding tools.

In one example, MRL may be implemented if a block has an MRL index other than 0, then the ISP coding mode can be inferred to be 0 and therefore ISP mode information may not be sent to the decoder. In another example, entropy coding coefficient group size may be selected if the sizes of the entropy coding subblocks have been modified so that they have 16 samples in all possible cases, as shown in Table 5. Note that the new sizes may only affect blocks produced by ISP in which one of the dimensions is less than 4 samples. In all other cases coefficient groups may keep the 4×4 dimensions.

Additionally or alternatively, with respect to coded block flag (CBF) coding, it is assumed to have at least one of the sub-partitions has a non-zero CBF. Hence, if n is the number of sub-partitions and the first n−1 sub-partitions have produced a zero CBF, then the CBF of the n-th sub-partition can be inferred to be 1. Transform size restriction: all ISP transforms with a length larger than 16 points can use the discrete cosine transform (DCT)-II. Multiple transform selection (MTS) flag: if a CU uses the ISP coding mode, the MTS CU flag may be set to 0 and it may not be sent to the decoder. Therefore, the encoder may not perform rate distortion (RD) tests for the different available transforms for each resulting sub-partition. The transform choice for the ISP mode may instead be fixed and selected according the intra mode, the processing order and the block size utilized. Hence, no signaling may be required, in this example.

For example, let t_(H) and t_(V) be the horizontal and the vertical transforms selected respectively for the w×h sub-partition, where w is the width and h is the height. Then the transform can be selected according to the following rules: If w=1 or h=1, then there may be no horizontal or vertical transform respectively. If w≥4 and w<16, t_(H)=discrete sine transform (DST)-VII, otherwise, t_(H)=DCT-II. If h≥4 and h≤16, t_(V)=DST-VII, otherwise, t_(V)=DCT-II.

In ISP mode, all 67 intra-prediction modes are allowed. PDPC can also be applied if corresponding width and height is at least 4 samples long. In addition, the reference sample filtering process (reference smoothing) and the condition for intra interpolation filter selection may not exist anymore, and Cubic (DCT-IF) filter can be applied for fractional position interpolation in ISP mode.

FIG. 19 is an example of a diagram 1900 of matrix weighted intra-prediction process (MIP) for VVC. For predicting the samples of a rectangular block of width W and height H, −MIP takes one line of H reconstructed neighboring boundary samples left of the block and one line of W reconstructed neighboring boundary samples above the block as input. If the reconstructed samples are unavailable, they can be generated as in the conventional intra-prediction.

Among the boundary samples, four samples or eight samples can be selected by averaging based on block size and shape. Specifically, the input boundaries bdry^(top) and bdry^(left) are reduced to smaller boundaries bdry_(red) ^(top) and bdry_(red) ^(left) by averaging neighboring boundary samples according to predefined rule depends on block size. Then, the two reduced boundaries bdry_(red) ^(top) and bdry_(red) ^(left) can be concatenated to a reduced boundary vector bdry_(rea) which is thus of size four for blocks of shape 4×4 and of size eight for blocks of all other shapes. If mode refers to the MIP-mode, this concatenation is defined as follows:

$\begin{matrix} {{bdry}_{red} = \left\{ \begin{matrix} \left\lbrack {{bdry}_{red}^{top},{bdry}_{red}^{left}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}} \\ \left\lbrack {{bdry}_{red}^{left},{bdry}_{red}^{top}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}} \\ \left\lbrack {{bdry}_{red}^{top},{bdry}_{red}^{left}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 10}} \\ \left\lbrack {{bdry}_{red}^{left},{bdry}_{red}^{top}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 10}} \\ \left\lbrack {{bdry}_{red}^{top},{bdry}_{red}^{left}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} < 6} \\ \left\lbrack {{bdry}_{red}^{left},{bdry}_{red}^{top}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 6.} \end{matrix} \right.} & {{Equation}\mspace{14mu} 8} \end{matrix}$

A matrix vector multiplication, followed by addition of an offset, is carried out with the averaged samples as an input. The result is a reduced prediction signal on a subsampled set of samples in the original block. Out of the reduced input vector bdry_(red) a reduced prediction signal pred_(red), which is a signal on the down-sampled block of width W_(red) and height H_(red) is generated. Here, W_(red) and H_(red) are defined as:

$\begin{matrix} {W_{red} = \left\{ {{\begin{matrix} 4 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} \leq 8} \\ {\min\left( {W,8} \right)} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8} \end{matrix}H_{red}} = \left\{ \begin{matrix} 4 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} \leq 8} \\ {\min\left( {H,8} \right)} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8} \end{matrix} \right.} \right.} & {{Equation}\mspace{14mu} 9} \end{matrix}$

The reduced prediction signal pred_(red) may be computed by calculating a matrix vector product and adding an offset: pred_(red) =A·bdry_(red) +b   Equation 10

Here, A is a matrix that has W_(red)·H_(red) rows and 4 columns if W=H=4 and 8 columns in all other cases. b is a vector of size W_(red)·H_(red). The matrix A and the offset vector b are taken from one of the sets S₀, S₁, S₂. One defines an index idx=idx(W,H) as follows:

$\begin{matrix} {{{idx}\left( {W,H} \right)} = \left\{ \begin{matrix} 0 & {{{for}\mspace{14mu} W} = {H = 4}} \\ 1 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = 8} \\ 2 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8.} \end{matrix} \right.} & {{Equation}\mspace{14mu} 11} \end{matrix}$

Here, each coefficient of the matrix A is represented with 8 bit precision. The set S₀ consists of 16 matrices A₀ ^(i), i∈{0, . . . , 15} each of which has 16 rows and 4 columns and 16 offset vectors b₀ ^(i), i∈{0, . . . , 16} each of size 16. Matrices and offset vectors of that set are used for blocks of size 4×4. The set S_(i) consists of 8 matrices A₁ ^(i), i∈{0, . . . , 7}, each of which has 16 rows and 8 columns and 8 offset vectors b₁ ^(i), i∈{0, . . . , 7} each of size 16. The set S₂ consists of 6 matrices A₂ ^(i), i∈{0, . . . , 5}, each of which has 64 rows and 8 columns and of 6 offset vectors b₂ ^(i), i∈{0, . . . , 5} of size 64.

In some examples, the prediction signal at the remaining positions may be generated from the prediction signal on the subsampled set by linear interpolation which is a single step linear interpolation in each direction. The interpolation can be firstly performed in the horizontal direction and then in the vertical direction regardless of block shape or block size.

For each CU in intra mode, a flag indicating whether an MIP mode may be to be applied or not is sent. If an MIP mode is to be applied, MIP mode (predModeIntra) may be signalled. For an MIP mode, a transposed flag (isTransposed), which determines whether the mode is transposed, and MIP mode ID (modeId), which determines which matrix is to be used for the given MIP mode, can be derived as follows isTransposed=predModeIntra&1 modeId=predModeIntra>>1   Equation 12

MIP coding mode may be harmonized with other coding tools by considering following aspects: (1) low-frequency non-separable transform (LFNST) is enabled for MIP on large blocks. Here, the LFNST transforms of planar mode are used; (2) the reference sample derivation for MIP is performed exactly or at least similarly as for the conventional intra-prediction modes; (3) for the up-sampling step used in the MIP-prediction, original reference samples are used instead of down-sampled ones; (4) clipping is performed before up-sampling and not after up-sampling; (5) MIP may be allowed up to 64×64 regardless of the maximum transform size. In some aspects, the number of MIP modes may be 32 for sizeId=0, 16 for sizeId=1 and 12 for sizeId=2.

In joint exploration model (JEM)-2.0 intra modes are extended to 67 from 35 modes in HEVC, and they are derived at encoder and explicitly signalled to decoder. A significant amount of overhead is spent on intra mode coding in JEM-2.0. For example, the intra mode signaling overhead may be up to 5-10% of overall bitrate in all intra coding configuration. This contribution proposes the decoder-side intra mode derivation approach to reduce the intra mode coding overhead while keeping prediction accuracy. To reduce the overhead of intra mode signaling, a decoder-side intra mode derivation (DIMD) approach, which may be used by video decoders 124, 300, 400 in decoding video. In accordance with aspects of the present disclosure, instead of signaling intra mode explicitly, the information can be derived at both encoder and decoder from the neighboring reconstructed samples of current block. The intra mode derived by DIMD may be used in two ways, for example: 1) For 2N×2N CUs, the DIMD mode is used as the intra mode for intra-prediction when the corresponding CU-level DIMD flag is turned on; 2) For N×N CUs, the DIMD mode is used to replace one candidate of the existing MPM list to improve the efficiency of intra mode coding.

FIG. 20 is an example of a diagram 2000 of a template based intra mode derivation where the target denotes the current block (of block size N) for which intra-prediction mode is to be estimated. The template (indicated by the patterned region in FIG. 20 ) specifies a set of already reconstructed samples, which are used to derive the intra mode. The template size is denoted as the number of samples within the template that extends to the above and the left of the target block, i.e., L. In some implementations, a template size of 2 (i.e., L=2) can be used for 4×4 and 8×8 blocks and a template size of 4 (i.e., L=4) can be used for 16×16 and larger blocks. The reference of template (indicated by the dotted region in FIG. 20 ) can refer to a set of neighboring samples from above and left of the template, as defined by JEM-2.0. Unlike the template samples which are always from reconstructed region, the reference samples of template may not be reconstructed yet when encoding/decoding the target block. In this case, the existing reference samples substitution algorithm of JEM-2.0 is utilized to substitute the unavailable reference samples with the available reference samples.

For each intra-prediction mode, the DIMD calculates the absolute difference (SAD) between the reconstructed template samples and its prediction samples obtained from the reference samples of the template. The intra-prediction mode that yields the minimum SAD may be selected as the final intra-prediction mode of the target block.

For intra 2N×2N CUs, the DIMD can be used as one additional intra mode, which can be adaptively selected by comparing the DIMD intra mode with the optimal normal intra mode (i.e., being explicitly signalled). One flag is signalled for each intra 2N×2N CU to indicate the usage of the DIMD. If the flag is one, then the CU can be predicted using the intra mode derived by DIMD; otherwise, the DIMD is not applied and the CU is predicted using the intra mode explicitly signalled in the bit-stream. When the DIMD is enabled, chroma components can reuse the same intra mode as that derived for luma component, i.e., DM mode.

Additionally, for each DIMD-coded CU, the blocks in the CU can adaptively select to derive their intra modes at either PU-level or TU-level. Specifically, when the DIMD flag is one, another CU-level DIMD control flag can be signalled to indicate the level at which the DIMD is performed. If this flag is zero, this can indicate that the DIMD is performed at the PU level and all the TUs in the PU use the same derived intra mode for their intra-prediction; otherwise if the DIMD control flag is one, this can indicate that the DIMD is performed at the TU level and each TU in the PU derives its own intra mode.

Further, when the DIMD is enabled, the number of angular directions increases to 129, and the DC and planar modes still remain the same. To accommodate the increased granularity of angular intra modes, the precision of intra interpolation filtering for DIMD-coded CUs increases from 1/32-pel to 1/64-pel. Additionally, in order to use the derived intra mode of a DIMD coded CU as MPM candidate for neighboring intra blocks, those 129 directions of the DIMD-coded CUs can be converted to “normal” intra modes (i.e., 65 angular intra directions) before they are used as MPM.

In some aspects, intra modes of intra N×N CUs are signalled. However, to improve the efficiency of intra mode coding, the intra modes derived from DIMD are used as MPM candidates for predicting the intra modes of four PUs in the CU. In order to not increase the overhead of MPM index signaling, the DIMD candidate can be placed at the first place in the MPM list and the last existing MPM candidate can be removed. Also, a pruning operation can be performed such that the DIMD candidate may not be added to the MPM list if it is redundant.

In order to reduce encoding/decoding complexity, one straightforward fast intra mode search algorithm is used for DIMD. Firstly, one initial estimation process can be performed to provide a good starting point for intra mode search. Specifically, an initial candidate list can be created by selecting N fixed modes from the allowed intra modes. Then, the SAD can be calculated for all the candidate intra modes and the one that minimizes the SAD can be selected as the starting intra mode. To achieve a good complexity/performance trade-off, the initial candidate list can include 11 intra modes, including DC, planar and every 4-th mode of the 33 angular intra directions as defined in HEVC, i.e., intra modes 0, 1, 2, 6, 10 . . . 30, 34.

If the starting intra mode is either DC or planar, it can be used as the DIMD mode. Otherwise, based on the starting intra mode, one refinement process can then be applied where the optimal intra mode is identified through one iterative search. In the iterative search, at each iteration, the SAD values for three intra modes separated by a given search interval can be compared and the intra mode that minimizes the SAD can be maintained. The search interval can then be reduced to half, and the selected intra mode from the last iteration can serve as the center intra mode for the current iteration. For the current DIMD implementation with 129 angular intra directions, up to 4 iterations can be used in the refinement process to find the optimal DIMD intra mode.

In some examples, transmitting of the luma intra-prediction mode in the bitstream can be avoided. This is done by deriving the luma intra mode using previously encoded/decoded pixels, in an identical fashion at the encoder and at the decoder. This process defines a new coding mode called DIMD, whose selection signalled in the bitstream for intra coded blocks using a flag. DIMD can compete with other coding modes at the encoder, including the classic Intra coding mode (where the intra-prediction mode is coded). Note that in one example, DIMD may only apply to luma. For chroma, classical intra coding mode may apply. As done for other coding modes (classical intra, inter, merge, etc.), a rate-distortion cost can be computed for the DIMD mode, and can then be compared to the coding costs of other modes to decide whether to select it as final coding mode for a current block.

At the decoder side, the DIMD flag can be first parsed, if present. If the DIMD flag is true, the intra-prediction mode can be derived in the reconstruction process using the same previously encoded neighboring pixels. If not, the intra-prediction mode can be parsed from the bitstream as in classical intra coding mode.

To derive the intra-prediction mode for a block, a set of neighboring pixels may be first selected on which a gradient analysis is performed. For normativity purposes, these pixels can be in the decoded/reconstructed pool of pixels. FIG. 21 is an example of a diagram 2100 of a template of a set of chosen pixels on which a gradient analysis may be performed based on intra-prediction mode derivation. As shown in FIG. 21 , a template surrounding the current block is chosen by T pixels to the left, and T pixels above. For example, T may have a value of 2.

Next, a gradient analysis is performed on the pixels of the template. This can facilitate determining a main angular direction for the template, which can be assumed to have a high chance to be identical to the one of the current block. Thus, a simple 3×3 Sobel gradient filter can be used, defined by the following matrices that may be convoluted with the template:

$M_{x} = {{\begin{bmatrix} {- 1} & 0 & 1 \\ {- 2} & 0 & 2 \\ {- 1} & 0 & 1 \end{bmatrix}\mspace{14mu}{and}\mspace{20mu} M_{y}} = \begin{bmatrix} {- 1} & {- 2} & {- 1} \\ 0 & 0 & 0 \\ 1 & 2 & 1 \end{bmatrix}}$

For each pixel of the template, each of these two matrices with the 3×3 window centered around the current pixel can be point-by-point multiplied and composed of its 8 direct neighbors, and the result can be is summed. Thus, two values G_(x) (from the multiplication with M_(x)), and G_(y) (from the multiplication with M_(y)) corresponding to the gradient at the current pixel can be obtained, in the horizontal and vertical direction respectively.

FIG. 22 is an example of a diagram of a convolution of a 3×3 Sobel gradient filter with the template in accordance with aspects of the present disclosure. In some examples, the pixel 2210 is the current pixel. Template pixels 2220 (including the current pixel 2210) are pixels on which the gradient analysis is possible. Unavailable pixels 2230 are pixels on which the gradient analysis is not possible due to lack of some neighbors. Reconstructed pixels 2240 are available pixels outside of the considered template, used in the gradient analysis of the template pixels 2220. In case a reconstructed pixel 2240 is not available (due to blocks being too close to the border of the picture for instance), the gradient analysis of all template pixels 2220 that use the unavailable reconstructed pixel 2240 is not performed.

For each template pixel 2220, the intensity (G) and the orientation (O) of the gradient using G_(x) and G_(y) are calculated as such:

$G = {{{G_{x}} + {{G_{y}}\mspace{14mu}{and}\mspace{14mu} O}} = {a{\tan\left( \frac{G_{y}}{G_{x}} \right)}}}$

Note that a fast implementation of the a tan function is proposed. The orientation of the gradient can then be converted into an intra angular prediction mode, used to index a histogram (first initialized to zero). The histogram value at that intra angular mode is increased by G. Once all the template pixels 2220 in the template have been processed, the histogram can include cumulative values of gradient intensities, for each intra angular mode. The mode that shows the highest peak in the histogram can be selected as intra-prediction mode for the current block. If the maximum value in the histogram is 0 (meaning no gradient analysis was able to be made, or the area composing the template is flat), then the DC mode can be selected as intra-prediction mode for the current block.

For blocks that are located at the top of CTUs, the gradient analysis of the pixels located in the top part of the template is not performed. The DIMD flag is coded using three possible contexts, depending on the left and above neighboring blocks, similarly to the Skip flag coding. Context 0 corresponds to the case where none of the left and above neighboring blocks are coded with DIMD mode, context 1 corresponds to the case where only one neighboring block is coded with DIMD, and context 2 corresponds to the case where both neighbors are DIMD-coded. Initial symbol probabilities for each context are set to 0.5.

One advantage that DIMD offers over classical intra mode coding is that the derived intra mode can have a higher precision, allowing more precise predictions at no additional cost as it is not transmitted in the bitstream. The derived intra mode spans 129 angular modes, hence a total of 130 modes including DC (e.g., the derived intra mode may not be planar in aspects described herein). The classical intra coding mode is unchanged, i.e., the prediction and mode coding still use 67 modes.

The required changes to Wide Angle Intra-prediction and simplified PDPC were performed to accommodate for prediction using 129 modes. Note that only the prediction process uses the extended intra modes, meaning that for any other purpose (deciding whether to filter the reference samples for instance), the mode can be converted back to 67-mode precision.

In the DIMD mode, the luma intra mode is derived during the reconstruction process, just prior to the block reconstruction. This is done to avoid a dependency on reconstructed pixels during parsing. However, by doing so, the luma intra mode of the block may be undefined for the chroma component of the block, and for the luma component of neighboring blocks. This can cause an issue because for chroma, a fixed mode candidate list is defined. Usually, if the luma mode equals one of the chroma candidates, that candidate may be replaced with the vertical diagonal (VDIA_IDX) intra mode. As in DIMD, the luma mode is unavailable, the initial chroma mode candidate list is not modified.

In classical intra mode, where the luma intra-prediction mode is to be parsed from the bitstream, an MPM list is constructed using the luma intra modes of neighboring blocks, which can be unavailable if those blocks were coded using DIMD. In this case, for example, DIMD-coded blocks can be treated as inter blocks during MPM list construction, meaning they are effectively considered unavailable.

Entropy coding may be a form of lossless compression used at the last stage of video encoding (and the first stage of video decoding), after the video has been reduced to a series of syntax elements. Syntax elements describe how the video sequence can be reconstructed at the decoder. This includes the method of prediction (e.g., spatial or temporal prediction, intra-prediction mode, and motion vectors) and prediction error, also referred to as residual. Arithmetic coding is a type of entropy coding that can achieve compression close to the entropy of a sequence by effectively mapping the symbols (i.e., syntax elements) to codewords with a non-integer number of bits. Context-adaptive binary arithmetic coding (CABAC) involves three main functions: binarization, context modeling, and arithmetic coding. Binarization maps the syntax elements to binary symbols (bins). Context modeling estimates the probability of the bins. Finally, arithmetic coding compresses the bins to bits based on the estimated probability.

Several different binarization processes are used in VVC, such as the truncated Rice (TR) binarization process, the truncated binary binarization process, the k-th order Exp-Golomb (EGk) binarization process and the fixed-length (FL) binarization process.

Context modeling provides an accurate probability estimate required to achieve high coding efficiency. Accordingly, it is highly adaptive and different context models can be used for different bins and the probability of that context model is updated based on the values of the previously coded bins. Bins with similar distributions often share the same context model. The context model for each bin can be selected based on the type of syntax element, bin position in syntax element (binIdx), luma/chroma, neighboring information, etc. A context switch can occur after each bin.

Arithmetic coding may be based on recursive interval division. A range, with an initial value of 0 to 1, is divided into two subintervals based on the probability of the bin. The encoded bits provide an offset that, when converted to a binary fraction, selects one of the two subintervals, which indicates the value of the decoded bin. After every decoded bin, the range is updated to equal the selected subinterval, and the interval division process repeats itself. The range and offset have limited bit precision, so renormalization may be used whenever the range falls below a certain value to prevent underflow. Renormalization can occur after each bin is decoded. Arithmetic coding can be done using an estimated probability (context coded), or assuming equal probability of 0.5 (bypass coded). For bypass coded bins, the division of the range into subintervals can be done by a shift, whereas a look up table may be used for the context coded bins.

FIG. 23 is a schematic diagram 2300 of intra mode coding with greater than 67 intra-prediction modes to capture the arbitrary edge directions presented in natural video. In some examples, the number of directional intra modes may be extended from 67, as used in VVC, to 129 while the planar and the DC modes remain the same.

In one example, the pre-defined IPMs may be the IPMs have denser directions than conventional IPMs (e.g., IPMs denoted by the dashed lines in FIG. 23 ). In one example, the N1 IPMs may be partial or full of the MPMs for the current block. In one example, some pre-defined intra-prediction modes which are not in MPMs may also be contained in the given IPM candidate set.

In one example, one or more IPMs from DC/Planar/horizontal/vertical/diagonal top-right/diagonal bottom-left/diagonal top-left modes may be contained in the given IPM set.

In one example, one or more IPMs denoted by the dashed lines in FIG. 23 may be contained in the given IPM set.

In one example, N1 may be equal to or larger than N2 when one or more IPMs denoted by the dashed red lines are contained in the given IPM set.

In one example, N1 may be equal to or larger than N2.

FIGS. 24-31 illustrate examples of templates that may be formed from one or more sub-templates. As discussed in further detail below, the template for a block may be selected for the specific block. For instance, the template may be selected based on decoded information about the specific block or based on availability of the sub-templates for the specific block. Although several examples are illustrated, other templates may be selected based on different combinations of the sub-templates.

FIG. 24 is a diagram of an example of a template 2400 including a left-above sub-template 2420 (Template-LA). The template 2400 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The left-above sub-template 2420 may include left-above neighboring samples that are located both to the left of the block 2410 and above the block 2410. The left-above sub-template 2420 may have dimensions of L1 samples horizontally and L2 samples vertically. L1 and L2 may be defined for the block 2410, a slice including the block 2410, or a picture including the block 2410.

FIG. 25 is a diagram of an example of a template 2500 including a left sub-template 2440 (Template-L) and an above sub-template 2430 (Template-A). The template 2500 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may be adjacent the top edge of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may be adjacent the top edge of the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically.

FIG. 26 is a diagram of an example of a template 2600 including the above sub-template 2430 (Template-A). The template 2600 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically.

FIG. 27 is a diagram of an example of a template 2700 including a left sub-template (Template-L). The template 2700 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically.

FIG. 28 is a diagram of an example of a template 2800 including the left sub-template 2440 (Template-L) and a left-below sub-template 2450 (Template-LB). The template 2800 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically. The left-below sub-template 2450 may include samples that are located both to the left of the block 2410 and below the block 2410. The left-below sub-template 2450 may have dimensions of L1 samples horizontally and N samples vertically.

FIG. 29 is a diagram of an example of a template 2900 including the above sub-template 2430 (Template-A) and a right-above sub-template 2460 (Template-RA). The template 2900 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically. The right-above sub-template 2460 may include samples located both above the block 2410 and to the right of the block 2410. The right-above sub-template 2460 may have dimensions of M samples horizontally and L2 samples vertically.

FIG. 30 is a diagram of an example of a template 3000 including the left sub-template 2440, the left-below sub-template 2450, the above sub-template 2430, and the right-above sub-template 2460. The template 3000 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically. The right-above sub-template 2460 may include samples located above and to the right of the block 2410. The right-above sub-template 2460 may have dimensions of M samples horizontally and L2 samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically. The left-below sub-template 2450 may include samples located to the left of the block 2410 and below the block 2410. The left-below sub-template 2450 may have dimensions of L1 samples horizontally and N samples vertically.

FIG. 31 is a diagram of an example of a template 3100 including the left-above sub-template 2420, the left sub-template 2440, the left-below sub-template 2450, the above sub-template 2430, and the right-above sub-template 2460. The template 3100 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The left-above sub-template 2420 may include samples located to the left and above the block 2410. The left-above sub-template 2420 may have dimensions of L1 samples horizontally and L2 samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically. The right-above sub-template 2460 may include samples located above and to the right of the block 2410. The right-above sub-template 2460 may have dimensions of M samples horizontally and L2 samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically. The left-below sub-template 2450 may include samples located to the left of and below the block 2410. The left-below sub-template 2450 may have dimensions of L1 samples horizontally and N samples vertically.

FIG. 32 is a diagram of an example of a template 3200 including a left-above sub-template 2420, a left sub-template 2440, a left-below sub-template 2450, an above sub-template 2430, and a right-above sub-template 2460 that are spaced apart from a block. The example template 3200 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. In contrast to the sub-templates in FIGS. 24-31 , the sub-templates in FIG. 32 may be spaced apart from the block 2410. For example, the left-above sub-template 2420, the left sub-template 2440, and the left-below sub-template 2450 may be spaced horizontally apart from the block 2410 by a gap 3220. The gap 3220 may have a horizontal dimension of L3 samples. The left-above sub-template 2420, the above sub-template 2430, and the right-above sub-template 2460 may be spaced vertically apart from the block 2410 by a gap 3210. The gap 3210 may have a vertical dimension of L4 samples. In an aspect, each of the sub-templates 2420, 2430, 2440, 2450, 2460 may have dimensions that are the same as a corresponding sub-template 2420, 2430, 2440, 2450, 2460 in FIGS. 24-31 . Accordingly, in FIG. 32 , the locations of the sub-templates 2420, 2430, 2440, 2450, 2460 are different, but the size of the sub-templates 2420, 2430, 2440, 2450, 2460 may be the same as in FIGS. 24-31 .

FIG. 33 is a diagram of examples of template-reference samples 3310 for a template 3300 including a left-above sub-template 2420, a left sub-template 2440, and an above sub-template 2430. The example template 3300 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The left-above sub-template 2420 may include samples located to the left and above the block 2410. The left-above sub-template 2420 may have dimensions of L1 samples horizontally and L2 samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically. The template-reference samples 3310 may be a single row of samples located above the template 3300 and a single column of samples located to the left of the template 3300. The row of samples may have a length of 2(L1+M)+1. The column of samples may have a height of 2(L2+N)+1.

FIG. 34 is a diagram of example template-reference samples 3410 for the template 2500 including the left sub-template 2440 and the above sub-template 2430. The example template 2500 may be selected for a block 2410, which may have dimensions of M samples horizontally and N samples vertically. The above sub-template 2430 may include samples located above the block 2410. The above sub-template 2430 may have dimensions of M samples horizontally and L2 samples vertically. The left sub-template 2440 may include samples located to the left of the block 2410. The left sub-template 2440 may have dimensions of L1 samples horizontally and N samples vertically. The template-reference samples may include one or more lines (e.g., rows or columns) of samples. For example, the template-reference samples 3410 may include a single row of samples located above the template 2500 and a single column of samples located to the left of the template 2500. The row of samples may have a length of 2(L1+M)+1. The column of samples may have a height of 2(L2+N)+1.

FIG. 35 is a diagram of example template-reference samples 3510 for the template 2600 including the above sub-template 2430. The template-reference samples 3510 may be a single row of samples located above the template 2600 and a single column of samples located to the left of the template 2600. The row of samples may have a length of 2M+1. The column of samples may have a height of 2(L2+N)+1.

FIG. 36 is a diagram of example template-reference samples 3610 for the template 2700 including the left sub-template 2440. The template-reference samples 3610 may be a single row of samples located above the template 2700 and a single column of samples located to the left of the template 2700. The row of samples may have a length of 2(L1+M)+1. The column of samples may have a height of 2N+1.

FIG. 37 is a diagram of example template-reference samples 3710 for the template 2600 including the above sub-template 2430. The template-reference samples 3710 may be a single row of samples located above the template 2600 and a single column of samples located to the left of the template 2600. The row of samples may have a length of 2(L1+M)+1. The column of samples may have a height of 2(L2+N)+1. Because the template 2600 does not include the left-above sub-template 2420 or the left sub-template 2440, the column of samples may be spaced from the template 2600 by a horizontal gap 3720 with a width of L1.

FIG. 38 is a diagram of example template-reference samples 3810 for the template 2700 including the left sub-template 2440. The template-reference samples 3810 may be a single row of samples located above the template 2700 and a single column of samples located to the left of the template 2700. The row of samples may have a length of 2(L1+M)+1. The column of samples may have a height of 2(L2+N)+1. Because the template 2700 does not include the left-above sub-template 2420 or the above sub-template 2430, the row of samples may be spaced from the template 2700 by a vertical gap 3820 with a height of L2.

FIG. 39 is a diagram of example template-reference samples 3910 for the template 2500 including the above sub-template 2430 and the left sub-template 2440. The template-reference samples 3910 may include a single column of samples located to the left of the template 2500. The column of samples may have a height of 2(L2+N)+1. Instead of a single row of template-reference samples, a portion 3920 of the row may be moved to a second row 3930 that is adjacent the left sub-template 2440. The portion 3920 may include L1 samples. The remaining portion in the first row may have a length of 2M+L1+1. In an aspect, selecting template-reference samples that are adjacent a sub-template included within the template may improve the prediction of the template.

FIG. 40 is a diagram of example template-reference samples 4010 for the template 2500 including the above sub-template 2430 and the left sub-template 2440. The template-reference samples 4010 may include a single row of samples located above the template 2500. The row of samples may have a length of 2(L1+M)+1. Instead of a single column of template-reference samples, a portion 4020 of the column may be moved to a second row 4030 that is adjacent the above sub-template 2430. The portion 4020 may include L2 samples. The remaining portion in the first column may have a height of 2N+L2+1. In an aspect, selecting template-reference samples that are adjacent a sub-template included within the template may improve the prediction of the template. In another aspect, both of the portion 3920 and the portion 4020 may be moved to the second row 3930 and the second row 4030, respectively.

Referring to FIGS. 41-43 , in operation, computing device 4102 may perform a method 4300 of video processing, via execution of decoding component 4110 by processor 4104 and/or memory 4106, video decoder 124, video decoder 300, or HEVC video encoder and decoder 400. In addition, computing device 4202 may perform the method 4300 of video processing, via execution of encoding component 4210 by processor 4104 and/or memory 4106, video encoder 114, or HEVC video encoder and decoder 400.

At block 4302, the method 4300 includes determining, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one IPM is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, the DIMD detection component 4112, and/or the DIMD component 4114 may be configured to or may comprise means for determining, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one IPM is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit.

For example, the DIMD detection component 4112 may be configured to determine to apply decoder-side intra mode derivation to a decoding unit of an encoded bitstream 4120. As used herein, a decoding unit may refer to a block, picture, sub-picture, tile, slice, CTU, video processing and distribution unit (VPDU), CTU row, CU, or PU. In some aspects, the DIMD detection component 4112 may determine whether to apply DIMD to the decoding unit based on decoded information. For example, the decoding video unit may be a current block being processed in a decoding process. Further, the DIMD detection component 4112 may determine decoded information corresponding the block, and determine whether to apply DIMD to the block during the decoding process based on the decoded information.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on one or more attributes of the decoding unit (e.g., one or more dimensions of a block and/or a shape of the block as defined in the decoded information). For instance, a block width may be denoted as BW and a block height may be denoted as BH. Further, the DIMD detection component 4112 may apply DIMD to the block when the BW*BH>=T1, where T1 is a configured threshold (e.g., T1=16/64/256). In some other instances, the DIMD detection component 4112 may apply DIMD to the block when BW*BH<=T2, where T2 is a configured threshold (e.g., T2=16/64/256/1024). In another instance, the DIMD detection component 4112 may apply DIMD to the block when BW/BH or BH/BW<=T3, where T3 is a configured threshold (e.g., T3=4/8). In yet another instance, the DIMD detection component 4112 may apply DIMD to the block when BW/BH or BH/BW>=T4, where T4 is a configured threshold (e.g., T4=1).

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a block based on a slice type (e.g., I-slice, B-slice, or P-slice) or picture type of the block as defined in the decoded information. For instance, the DIMD detection component 4112 may apply DIMD to the block only when the slice type of the block is an I slice. In some other instances, the DIMD detection component 4112 may determine whether to apply DIMD to one or more temporal layers of the encoded bitstream 4120 when the decoded information indicates that hierarchical coding was employed during the encoding process.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on signaling. For instance, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on signaling in a sequence parameter set (SPS), picture parameter set (PPS), picture header, slice header, CTU, CU, and/or PU. Further, the signaling may correspond to a particular decoding unit (e.g., a block) or a plurality of decoding units.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on a DIMD indicator signaled as syntax element. Additionally, or alternatively, the syntax element may include a length of the IPM candidate set used to apply DIMD to the decoding unit. In some instances, the syntax element may be binarized using fix length coding, unary coding, truncated unary coding, Exp-Golomb coding, or coding a flag. In some other instances, the syntax element may be bypass coded. In yet still some other instances, the syntax element may be context coded. For instance, the syntax element may be based on decoded information. As described herein, the decoded information may be related to one or more attributes of a decoding unit, e.g., dimensions of a block, a function based on the dimensions of the block, a slice type of the block, picture type of the block, etc.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on the availability of one or more templates. For instance, the DIMD detection component 4112 may apply DIMD to a block based at least in part on the availability of templates and template-reference samples for deriving the IPM. In particular, the DIMD detection component 4112 may apply DIMD to a block based on one or more templates and template-reference samples associated with the block being available for deriving the IPM for the block. As used herein, in some aspects, a “template-reference sample” may refer to reconstructed samples used as a reference to derive predicted samples of a template.

As used herein, in some aspects, the “availability of a template” may refer to whether the template has been reconstructed, located inside the picture, sub-picture, tile, or slice, and/or located in the same video unit as the template and/or current block. As used herein, in some aspects, the “availability of a template-reference sample” may refer to whether a template-reference sample has been reconstructed, located inside the located inside the picture, sub-picture, tile, or slice, and/or located in the same video unit as the template and/or current block. In some aspects, the samples for a block may be considered unavailable when all of the templates and template-reference samples under consideration are unavailable or at least one of the templates and/or template-reference samples under consideration is unavailable.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD based on a relationship between the videos units including a current block, the plurality of templates associated with the current block, and the plurality of template-reference samples associated with the current block, respectively. Some examples of a video unit include PU, CU, VPDU, CTU, CTU row, CTU slice, CTU tile, or CTU/sub-picture. In some instances, the DIMD detection component 4112 may apply DIMD to a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are co-located within the same video unit.

In some other instances, the DIMD detection component 4112 may apply DIMD to a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are not co-located within the same video unit. Further, the DIMD component 4114 may perform DIMD using a default IPM when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the default IPM may include planar/DC/horizontal mode/vertical mode/diagonal top-right mode/diagonal bottom-left mode/diagonal top-left mode. In some other aspects, the default IPM may be derived from neighboring blocks of the current block. In yet still some other aspects, the default IPM may be derived from the decoded information. Additionally, or alternatively, the DIMD component 4114 may perform DIMD using a plurality of modified reference-template samples or a plurality of modified templates when the block, the plurality of templates (M2), and the plurality of template-reference samples (M1) are not co-located within the same video unit. In some aspects, the number of lines, rows, or columns (M1) of the reference-template samples to N1 and/or the number of lines, rows, or columns (M2) of the templates may be modified to N2 when the first video unit is different from the second video unit or/and the third video unit. In some examples, N1 is less than or equal to M1 (e.g., M1=4, N1=1 or M1=2, N1=1), and N2 is less than or equal to M2 (e.g., M2=4, N2=1 or M2=2, N2=1).

In some instances, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on an intra coding tool. As an example, the DIMD detection component 4112 may determine to apply DIMD based on the absence of signaling including information associated with an application of an intra coding tool to the current block. Alternatively, the DIMD detection component 4112 may determine not to apply DIMD based on the presence of signaling including information associated with an application of an intra coding tool to the current block and/or the absence of signaling indicating the application of DIMD to the current block. Some examples of an intra coding tool include intra sub-partitions (ISP), multiple reference line (MRL), cross-component linear model (CCLM) prediction mode, matrix weighted intra prediction (MIP), and/or position dependent intra prediction combination (PDPC).

Further, in some aspects, a first syntax element may indicate the use of a derived IPM and a second syntax element may indicate the use of an intra coding tool. For example, a first syntax element may indicate whether a derived IPM is used and a second syntax element may indicate whether ISP is used. Further, in some aspects, if one of the syntax elements are determined using context coding, the context coded syntax element may be based on the other syntax element. For example, if the derived IPM is used with ISP and the first syntax element is context coded, the context of the first syntax element may be based on the second syntax element. Further, if the second syntax element is context coded, the context of the second syntax element may be based on the first syntax element. In some other examples, the syntax elements may not be based on each other.

In another example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, DIMD enabling component 4212, bitstream generating component 4214, and/or signaling component 4216 may be configured to or may comprise means for determining to apply decoder-side intra mode derivation (DIMD) to a unit of a bitstream.

For example, the determining at block 4302 may include determining to apply decoder-side intra mode derivation to a unit of an bitstream. In some aspects, a unit may include a block, picture, sub-picture, tile, slice, CTU, VPDU, CTU row, CU, or PU. Further, in some aspects, the DIMD enabling component 4212 may not enable DIMD for all of the blocks within the encoding unit. For example, the DIMD enabling component 4212 may enable DIMD for a first block within a CU and disable DIMD for a second block within the same CU.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on the dimensions of the block and/or a shape of the block of the plurality of pictures 4220. For instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width multiplied by the block height is larger than or equal to T1 (e.g., T1=16/64/256). In some other instances, the DIMD enabling component 4212 may enable DIMD for a block when the block width multiplied by the block height is less than or equal to T2 (such as T2=16/64/256/1024). In another instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width divided by the block height or the block height divided by block width is is less than or equal to T3 (such as T3=4/8). In yet another instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width divided by the block height or the block height divided by block width is larger than or equal to T4 (such as T4=1).

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on a slice type or picture type of the block. For instance, the DIMD enabling component 4212 may enable DIMD for the block only when the slice type of the block is an I-slice. In some other instances, the DIMD enabling component 4212 may enable DIMD for one or more temporal layers when hierarchical coding is being employed by the encoding component 4210 to generate the encoded bitstream 4222.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on the availability of one or more templates. For instance, the DIMD enabling component 4212 may enable DIMD for the block based at least in part on the availability of templates and template-reference samples for deriving the IPM. In particular, DIMD enabling component 4212 may enable DIMD for the block based on one or more templates and/or one or more template-reference samples associated with a block being available for deriving the IPM for the block. In some aspects, the samples for a block may be considered unavailable when all of the templates and template-reference samples under consideration are unavailable or at least one of the templates and/or template-reference samples under consideration is unavailable.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on a relationship between the videos units including a block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the block, respectively. In some instances, the DIMD enabling component 4212 may enable DIMD for a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are co-located within the same video unit.

In some other instances, the DIMD enabling component 4212 may enable DIMD for a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are not co-located within the same video unit. Further, DIMD may be performed using a default IPM when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the default IPM may include Planar/DC/horizontal mode/vertical mode/diagonal top-right mode/diagonal bottom-left mode/diagonal top-left mode. In some other aspects, the default IPM may be derived from neighboring blocks to the current block. Additionally, or alternatively, DIMD may be performed using a plurality of modified reference-template samples or a plurality of modified templates when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the number of lines, rows, or columns (M1) of the reference-template samples to N1 and/or the number of lines, rows, or columns (M2) of the templates may be modified to N2 when the first video unit is different from the second video unit or/and the third video unit. In some examples, N1 is less than or equal to M1 (e.g., M1=4, N1=1 or M1=2, N1=1), and N2 is less than or equal to M2 (e.g., M2=4, N2=1 or M2=2, N2=1).

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on an intra coding tool. For instance, the DIMD detection component 4112 may determine to disable DIMD for a block based on the use of an intra coding tool that cannot be used with a derived IPM, or enable DIMD for a block based on the use of an intra coding tool that may be used with a derived IPM. Some examples of an intra coding tool include ISP, MRL, CCLM prediction mode, MIP, and/or PDPC.

Referring to FIG. 44 , at block 4404, the method 4400 includes performing the conversion based on the determining. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, and/or the DIMD component 4114 may be configured to or may comprise means for performing the conversion based on the determining.

For example, performing DIMD at block 4404 may include determining a derived IPM using a color component. As an example, the DIMD component 4114 may employ DIMD to generate a predictor block for a second color component from a first color component when reconstructing a decoding unit within the encoded bitstream 4120 to generate the decoded video data 4122 based on the DIMD detection component 4112 determining to apply DIMD to the decoding unit. In some aspects, the first component may be the same as the second component. Alternatively, in some other aspects, the first component may be different from the second component. For instance, the first component may be Y in the YCbCr format and the second component may be Cb or Cr in the YCbCr format. In another instance, the first component may be G in RGB format, and the second component may be B or R in the RGB format. In another instance, the first component may be Cb in the YCbCr format and the second component may be Y or Cr in the YCbCr format. In another instance, the first component may be B in RGB format and the second component may be G or R in the RGB format. In another instance, the first component may be Cr in the YCbCr format and the second component may be Y or Cb in the YCbCr format. In another instance, the first component may be R in RGB format and the second component may be G or B in the RGB format.

As another example, the video unit may be a chroma block, and the DIMD component 4114 may generate a predictor block for the chroma block from the corresponding luma block. In some aspects, DIMD component 4114 may employ a chroma derived mode (DM mode) to generate the predictor block for the chroma block. In some other examples, the video unit may be a luma block, and the DIMD component 4114 may generate a predictor block for the luma block from a corresponding chroma block.

As yet still another example, in some aspects, the DIMD component 4114 may determine an IPM candidate set for a first color component and determine a different IPM candidate set for a second color component. For instance, the DIMD component 4114 may derive an IPM for a luma block using an IPM candidate having a size that is different from the size of an IPM candidate set used for a corresponding chroma block. Alternatively, the size of an IPM candidate set used to derive an IPM for a luma block may be equal to the size of an IPM candidate set used for a chroma block.

In some examples, performing DIMD may include determining a derived IPM using previously coded video units. For instance, in some aspects, the DIMD component 4114 may be configured to derive an IPM for a current block using a plurality of IPMs used with respect to previously-coded blocks. In some examples, the DIMD component 4114 may be configured to generate a predictor block for a current block from an intra prediction mode of a previously-coded block. In one aspect, the derived IPM may be set equal to the most used intra mode for a plurality of blocks neighboring the current block. In some other examples, in some aspects, the DIMD component 4114 may be configured to derive an IPM for a current block using a plurality of IPMs used with respect to a region of previously-coded blocks.

In some instances, performing DIMD may include determining a derived IPM based on the gradients of a neighboring sample. For example, in some aspects, the DIMD component 4114 may be configured to determining a gradient value of a neighboring sample of a block; and generate a predictor block for the current block based on the gradient. In some aspects, the derived IPM may be derived from a direction with the largest amplitude. In some other aspects, the derived IPM may be set a default mode when a predefined number of directions have similar amplitudes. Some examples of the default mode may include DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, and/or diagonal top-left mode.

As described above, in some aspects, a derived IPM may be employed with an intra coding tool. For example, the derived IPM may be used with ISP. In some instances, the derived IPM may be applied to one or more parts of ISP to derive the predicted samples of the parts. In another instance, an individual IPM may be derived for each part of ISP. In some aspects, when deriving an individual IPM for each part of ISP, the derivation of IPM for each part may be same as the derivation of IPM for the whole block. In some other examples, when the derived IPM is used with ISP, the decoding component 4110 may apply one or more transforms to the current block. Some examples of transforms that may be applied to the block include MTS and/or LFNST. In some instances, when the derived intra mode is used with ISP, the decoding component 4110 may be limited to applying only one transform in MTS. For example, the decoding component 4110 may apply DCT X or DST Y may be applied, where X and Y are integers. As another example, the decoding component 4110 may apply LFNST with an index equal to Z, where Z is an integer. In some aspects, Z may be equal to 0.

Further, as another example, the derived IPM may be used with MRL. Further, in some aspects, when a derived IPM is used with MRL, application of MRL may be limited to a particular reference line. For instance, in some aspects, when a derived IPM is used with MRL, only the second or third reference line may be supported in MRL.

Further, as yet still another example, the derived IPM may be used with MIP. In some instances, the decoding component 4110 may implement an MIP derived from a plurality of templates, and the DIMD component 4114 may be configured to apply the MIP mode to the decoding unit (e.g., a block). In some aspects, the MIP mode as implemented by the decoding component 4110 may include a MIP mode index and/or MIP transposed flag.

As another example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, bitstream generating component 4214, and/or the signaling component 4216 may be configured to or may comprise means for performing the conversion based on the determining.

For example, the generating at block 4404 may include generating an encoded bitstream 4222 based on the plurality of video frames 4220, wherein the encoded bitstream 4222 may include signaling indicating the application of DIMD and/or the length of a IPM candidate set in response to the DIMD enabling component 4212 enabling the bitstream generating component 4214 to employ DIMD.

In some examples, the signaling component may 4216 may signal use of DIMD in response to the DIMD enabling component 4212 enabling DIMD. For instance, the signaling component 4216 may signal use of DIMD in a SPS, PPS, picture header, slice header, CTU, CU, and/or PU. Further, in some instances, the signaling component 4216 may signal a syntax element indicating the use of DIMD. In some aspects, the syntax element may indicate the application of a derived IPM to a color component.

In some examples, the syntax element may be binarized using fix length coding, unary coding, truncated unary coding, Exp-Golomb coding, CABAC coding, or coding a flag. In some other instances, the syntax element may be bypass coded. In yet still some other instances, the syntax element may be context coded. Further, the context may provide information corresponding to dimensions of a block, a slice type of a block, and/or one or more attributes of neighboring blocks of the block (e.g., left neighboring blocks, above neighboring blocks, left-below neighboring blocks, right-above neighboring blocks, and/or left-above neighboring blocks). Some attributes of the neighboring blocks may include whether the neighbouring blocks are intra coded, whether the neighbouring blocks are DIMD coded, one or more methods or tools applied to the neighboring blocks (e.g., ISP/MRL/MIP), and/or partition information corresponding to the neighboring blocks (e.g., dual or single tree, local dual tree or single tree).

Further, if the DIMD enabling component 4212 does not enable DIMD, the signaling component 4216 may not signal usage of DIMD for a particular encoding unit. For example, if a derived IPM cannot be used with a particular intra coding tool, then the signaling unit 4216 may not signal the usage of DIMD when the intra coding tool is applied to the current block. In addition, if a derived IPM cannot be used with a particular intra coding tool, then the signaling unit 4216 may not signal the usage of the intra coding tool when a derived IPM is applied to the current block.

In some examples, when a derived IPM is used with a particular intra coding tool, the signaling component 4216 may signal information corresponding to use of DIMD (e.g., information corresponding to the derived IPM) and information related to use of the particular intra coding tool. As an example, the signaling component may signal a first syntax element indicating that a derived IPM was used and a second syntax element indicating the use of an intra coding tool (e.g., ISP). Further, the signaling component 4216 may signal the information corresponding to the intra coding tool before or after information corresponding to the use of DIMD. For example, the signaling component 4216 may signal information related to a derived IPM (e.g., a DIMD flag/index) before or after information corresponding to MIP, ISP, and/or MRL within the encoded bitstream 4222.

In some aspects, when application of DIMD is permitted with respect to blocks having a particular intra coding tool applied (e.g., MIP, MRL, ISP), the signaling component 4216 may not signal an indication of use of the DIMD. Alternatively, when application of DIMD is not permitted with respect to blocks having a particular intra coding tool applied, the signaling component 4216 may signal an indication of use of the DIMD.

Referring to FIGS. 41, 42, and 44 , in operation, computing device 4102 may perform a method 4400 of video processing, via execution of decoding component 4110 by processor 4104 and/or memory 4106, video decoder 124, video decoder 300, or HEVC video encoder and decoder 400. In addition, computing device 4202 may perform a method 4400 of video processing, via execution of encoding component 4210 by processor 4104 and/or memory 4106, video encoder 114, or HEVC video encoder and decoder 400.

At block 4402, the method 4400 includes determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one IPM is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, the DIMD detection component 4112, and/or the DIMD component 4114 may be configured to or may comprise means for determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one IPM is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block.

For example, the DIMD detection component 4112 may be configured to determine to apply decoder-side intra mode derivation to a decoding unit of an encoded bitstream 4120. As used herein, a decoding unit may refer to a block, picture, sub-picture, tile, slice, CTU, VPDU, CTU row, CU, or PU. In some aspects, the DIMD detection component 4112 may determine whether to apply DIMD to the decoding unit based on decoded information. For example, the decoding unit may be a current block being processed in a decoding process. Further, the DIMD detection component 4112 may determine decoded information corresponding the block, and determine whether to apply DIMD to the block during the decoding process based on the decoded information.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on one or more attributes of the decoding unit (e.g., one or more dimensions of a block and/or a shape of the block as defined in the decoded information). For instance, a block width may be denoted as BW and a block height may be denoted as BH. Further, the DIMD detection component 4112 may apply DIMD to the block when the BW*BH>=T1, where T1 is a configured threshold (e.g., T1=16/64/256). In some other instances, the DIMD detection component 4112 may apply DIMD to the block when BW*BH<=T2, where T2 is a configured threshold (e.g., T2=16/64/256/1024). In another instance, the DIMD detection component 4112 may apply DIMD to the block when BW/BH or BH/BW<=T3, where T3 is a configured threshold (e.g., T3=4/8). In yet another instance, the DIMD detection component 4112 may apply DIMD to the block when BW/BH or BH/BW>=T4, where T4 is a configured threshold (e.g., T4=1).

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a block based on a slice type (e.g., I-slice, B-slice, or P-slice) or picture type of the block as defined in the decoded information. For instance, the DIMD detection component 4112 may apply DIMD to the block only when the slice type of the block is an I-slice. In some other instances, the DIMD detection component 4112 may determine whether to apply DIMD to one or more temporal layers of the encoded bitstream 4120 when the decoded information indicates that hierarchical coding was employed during the encoding process.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on signaling. For instance, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on signaling in a sequence parameter set (SPS), picture parameter set (PPS), picture header, slice header, CTU, CU, and/or PU. Further, the signaling may correspond to a particular decoding unit (e.g., a block) or a plurality of decoding units.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on a DIMD indicator signalled as syntax element. Additionally, or alternatively, the syntax element may include a length of the IPM candidate set used to apply DIMD to the decoding unit. In some instances, the syntax element may be binarized using fix length coding, unary coding, truncated unary coding, Exp-Golomb coding, or coding a flag. In some other instances, the syntax element may be bypass coded. In yet still some other instances, the syntax element may be context coded. For instance, the syntax element may be based on decoded information. As described herein, the decoded information may be related to one or more attributes of a decoding unit, e.g., dimensions of a block, a function based on the dimensions of the block, a slice type of the block, picture type of the block, etc.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on the availability of one or more templates. For instance, the DIMD detection component 4112 may apply DIMD to a block based at least in part on the availability of templates and template-reference samples for deriving the IPM. In particular, the DIMD detection component 4112 may apply DIMD to a block based on one or more templates and template-reference samples associated with the block being available for deriving the IPM for the block. As used herein, in some aspects, a “template-reference sample” may refer to reconstructed samples used as a reference to derive predicted samples of a template.

As used herein, in some aspects, the “availability of a template” may refer to whether the template has been reconstructed, located inside the picture, subpicture, tile, slice, and/or located in the same video unit as the template and/or current block. As used herein, in some aspects, the “availability of a template-reference sample” may refer to whether a template-reference sample has been reconstructed, located inside the picture/subpicture/tile/slice, and/or located in the same video unit as the template and/or current block. In some aspects, the samples for a block may be considered unavailable when all of the templates and template-reference samples under consideration are unavailable or at least one of the templates and/or template-reference samples under consideration is unavailable.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD based on a relationship between the videos units including a current block, the plurality of templates associated with the current block, and the plurality of template-reference samples associated with the current block, respectively. Some examples of a video unit include PU, CU, VPDU, CTU, CTU row, CTU slice, CTU tile, or CTU/sub-picture. In some instances, the DIMD detection component 4112 may apply DIMD to a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are co-located within the same video unit.

In some other instances, the DIMD detection component 4112 may apply DIMD to a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are not co-located within the same video unit. Further, the DIMD component 4114 may perform DIMD using a default IPM when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the default IPM may include a DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, or diagonal top-left mode. In some other aspects, the default IPM may be derived from neighboring blocks of the current block. In yet still some other aspects, the default IPM may be derived from the decoded information. Additionally, or alternatively, the DIMD component 4114 may perform DIMD using a plurality of modified reference-template samples or a plurality of modified templates when the block, the plurality of templates (M2), and the plurality of template-reference samples (M1) are not co-located within the same video unit. In some aspects, the number of lines, rows, or columns (M1) of the reference-template samples to N1 and/or the number of lines, rows, or columns (M2) of the templates may be modified to N2 when the first video unit is different from the second video unit or/and the third video unit. In some examples, N1 is less than or equal to M1 (e.g., M1=4, N1=1 or M1=2, N1=1), and N2 is less than or equal to M2 (e.g., M2=4, N2=1 or M2=2, N2=1).

In some instances, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on an intra coding tool. As an example, the DIMD detection component 4112 may determine to apply DIMD based on the absence of signaling including information associated with an application of an intra coding tool to the current block. Alternatively, the DIMD detection component 4112 may determine not to apply DIMD based on the presence of signaling including information associated with an application of an intra coding tool to the current block and/or the absence of signaling indicating the application of DIMD to the current block. Some examples of an intra coding tool include intra sub-partitions (ISP), multiple reference line (MRL), cross-component linear model (CCLM) prediction mode, matrix weighted intra prediction (MIP), and/or position dependent intra prediction combination (PDPC).

Further, in some aspects, a first syntax element may indicate the use of a derived IPM and a second syntax element may indicate the use of an intra coding tool. For example, a first syntax element may indicate whether a derived IPM is used and a second syntax element may indicate whether ISP is used. Further, in some aspects, if one of the syntax elements are determined using context coding, the context coded syntax element may be based on the other syntax element. For example, if the derived IPM is used with ISP and the first syntax element is context coded, the context of the first syntax element may be based on the second syntax element. Further, if the second syntax element is context coded, the context of the second syntax element may be based on the first syntax element. In some other examples, the syntax elements may not be based on each other.

As another example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, DIMD enabling component 4212, bitstream generating component 4214, and/or signaling component 4216 may be configured to or may comprise means for determining to apply decoder-side intra mode derivation to a unit of a bitstream.

For example, the determining at block 4402 may include determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one IPM is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block. In some aspects, an encoding unit may include a block, picture, sub-picture, tile, slice, CTU, VPDU, CTU row, CU, or PU. Further, in some aspects, the DIMD enabling component 4212 may not enable DIMD for all of the blocks within the encoding unit. For example, the DIMD enabling component 4212 may enable DIMD for a first block within a CU and disable DIMD for a second block within the same CU.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD for a block based on the dimensions of the block and/or a shape of the block of the plurality of pictures 4220. For instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width multiplied by the block height is larger than or equal to T1 (e.g., T1=16/64/256). In some other instances, the DIMD enabling component 4212 may enable DIMD for a block when the block width multiplied by the block height is less than or equal to T2 (such as T2=16/64/256/1024). In another instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width divided by the block height or the block height divided by block width is is less than or equal to T3 (such as T3=4/8). In yet another instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width divided by the block height or the block height divided by block width is larger than or equal to T4 (such as T4=1).

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD for a block based on a slice type or picture type of the block. For instance, the DIMD enabling component 4212 may enable DIMD for the block only when the slice type of the block is an I-slice. In some other instances, the DIMD enabling component 4212 may enable DIMD for one or more temporal layers when hierarchical coding is being employed by the encoding component 4210 to generate the encoded bitstream 4222.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on the availability of one or more templates. For instance, the DIMD enabling component 4212 may enable DIMD for the block based at least in part on the availability of templates and template-reference samples for deriving the IPM. In particular, DIMD enabling component 4212 may enable DIMD for the block based on one or more templates and/or one or more template-reference samples associated with a block being available for deriving the IPM for the block. In some aspects, the samples for a block may be considered unavailable when all of the templates and template-reference samples under consideration are unavailable or at least one of the templates and/or template-reference samples under consideration is unavailable.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on a relationship between the videos units including a block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the block, respectively. In some instances, the DIMD enabling component 4212 may enable DIMD for a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are co-located within the same video unit.

In some other instances, the DIMD enabling component 4212 may enable DIMD for a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are not co-located within the same video unit. Further, DIMD may be performed using a default IPM when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the default IPM may include a DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, or diagonal top-left mode. In some other aspects, the default IPM may be derived from neighboring blocks to the current block. Additionally, or alternatively, DIMD may be performed using a plurality of modified reference-template samples or a plurality of modified templates when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the number of lines, rows, or columns (M1) of the reference-template samples to N1 and/or the number of lines, rows, or columns (M2) of the templates may be modified to N2 when the first video unit is different from the second video unit or/and the third video unit. In some examples, N1 is less than or equal to M1 (e.g., M1=4, N1=1 or M1=2, N1=1), and N2 is less than or equal to M2 (e.g., M2=4, N2=1 or M2=2, N2=1).

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on an intra coding tool. For instance, the DIMD detection component 4112 may determine to disable DIMD for a block based on the use of an intra coding tool that cannot be used with a derived IPM, or enable DIMD for a block based on the use of an intra coding tool that may be used with a derived IPM. Some examples of an intra coding tool include ISP, MRL, CCLM prediction mode, MIP, and/or PDPC.

Referring to FIG. 44 , at block 4404, the method 4400 performing a conversion based on the determining, wherein a syntax element is presented in the bitstream to indicate related information of the prediction mode derivation tool. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, the DIMD detection component 4112, and/or the DIMD component 4114 may be configured to or may comprise means for performing a conversion based on the determining, wherein a syntax element is presented in the bitstream to indicate related information of the prediction mode derivation tool. For example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, bitstream generating component 4214, and/or the signaling component 4216 may be configured to or may comprise means for performing a conversion based on the determining, wherein a syntax element is presented in the bitstream to indicate related information of the prediction mode derivation tool.

For example, the generating at block 4404 may include generating an encoded bitstream 4222 based on the plurality of video frames 4220, wherein the encoded bitstream 4222 may include signaling indicating the application of DIMD and/or the length of a IPM candidate set in response to the DIMD enabling component 4212 enabling the bitstream generating component 4213 to employ DIMD.

In some examples, the signaling component may 4216 may signal use of DIMD in response to the DIMD enabling component 4212 enabling DIMD. For instance, the signaling component 4216 may signal use of DIMD in a SPS, PPS, picture header, slice header, CTU, CU, and/or PU. Further, in some instances, the signaling component 4216 may signal a syntax element indicating the use of DIMD. In some aspects, the syntax element may indicate the application of a derived IPM to a color component.

In some examples, the syntax element may be binarized using fix length coding, unary coding, truncated unary coding, Exp-Golomb coding, CABAC coding, or coding a flag. In some other instances, the syntax element may be bypass coded. In yet still some other instances, the syntax element may be context coded. Further, the context may provide information corresponding to dimensions of a block, a slice type of a block, and/or one or more attributes of neighboring blocks of the block (e.g., left neighboring blocks, above neighboring blocks, left-below neighboring blocks, right-above neighboring blocks, and/or left-above neighboring blocks). Some attributes of the neighboring blocks may include whether the neighbouring blocks are intra coded, whether the neighbouring blocks are DIMD coded, one or more methods or tools applied to the neighboring blocks (e.g., ISP/MRL/MIP), and/or partition information corresponding to the neighboring blocks (e.g., dual or single tree, local dual tree or single tree).

Further, if the DIMD enabling component 4212 does not enable DIMD, the signaling component 4216 may not signal usage of DIMD for a particular encoding unit. For example, if a derived IPM cannot be used with a particular intra coding tool, then the signaling unit 4216 may not signal the usage of DIMD when the intra coding tool is applied to the current block. In addition, if a derived IPM cannot be used with a particular intra coding tool, then the signaling unit 4216 may not signal the usage of the intra coding tool when a derived IPM is applied to the current block.

In some examples, when a derived IPM is used with a particular intra coding tool, the signaling component 4216 may signal information corresponding to use of DIMD (e.g., information corresponding to the derived IPM) and information related to use of the particular intra coding tool. As an example, the signaling component may signal a first syntax element indicating that a derived IPM was used and a second syntax element indicating the use of an intra coding tool (e.g., ISP). Further, the signaling component 4216 may signal the information corresponding to the intra coding tool before or after information corresponding to the use of DIMD. For example, the signaling component 4216 may signal information related to a derived IPM (e.g., a DIMD flag/index) before or after information corresponding to MIP, ISP, and/or MRL within the encoded bitstream 4222.

In some aspects, when application of DIMD is permitted with respect to blocks having a particular intra coding tool applied (e.g., MIP, MRL, ISP), the signaling component 4216 may not signal an indication of use of the DIMD. Alternatively, when application of DIMD is not permitted with respect to blocks having a particular intra coding tool applied, the signaling component 4216 may signal an indication of use of the DIMD.

Furthermore, in some aspects, the computing device 4102 (e.g., the DIMD detection component 4112) may identify the signalled information related to DIMD within the bitstream, and process the encoded bitstream 4120 using the DIMD component 4114 in accordance with the information related to DIMD. For instance, the computing device 4120 may determine a syntax element and/or decoded information associated with DIMD, and performing one or more decoding operations on the encoded bitstream 4120 based on the syntax element and/or decoded DIMD.

Referring to FIGS. 41, 42, and 45 , in operation, computing device 4102 may perform a method 4500 of video processing, via execution of decoding component 4110 by processor 4104 and/or memory 4106, video decoder 124, video decoder 300, or HEVC video encoder and decoder 400. In addition, computing device 4202 may perform a method 4500 of video processing, via execution of encoding component 4210 by processor 4104 and/or memory 4106, video encoder 114, or HEVC video encoder and decoder 400.

At block 4502, the method 4500 includes determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one IPM is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, the DIMD detection component 4112, and/or the DIMD component 4114 may be configured to or may comprise means for determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one IPM is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block.

For example, the DIMD detection component 4112 may be configured to determine to apply decoder-side intra mode derivation to a decoding unit of an encoded bitstream 4120. As used herein, a decoding unit may refer to a block, picture, sub-picture, tile, slice, CTU, VPDU, CTU row, CU, or PU. In some aspects, the DIMD detection component 4112 may determine whether to apply DIMD to the decoding unit based on decoded information. For example, the decoding unit may be a current block being processed in a decoding process. Further, the DIMD detection component 4112 may determine decoded information corresponding the block, and determine whether to apply DIMD to the block during the decoding process based on the decoded information.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on one or more attributes of the decoding unit (e.g., one or more dimensions of a block and/or a shape of the block as defined in the decoded information). For instance, a block width may be denoted as BW and a block height may be denoted as BH. Further, the DIMD detection component 4112 may apply DIMD to the block when the BW*BH>=T1, where T1 is a configured threshold (e.g., T1=16/64/256). In some other instances, the DIMD detection component 4112 may apply DIMD to the block when BW*BH<=T2, where T2 is a configured threshold (e.g., T2=16/64/256/1024). In another instance, the DIMD detection component 4112 may apply DIMD to the block when BW/BH or BH/BW<=T3, where T3 is a configured threshold (e.g., T3=4/8). In yet another instance, the DIMD detection component 4112 may apply DIMD to the block when BW/BH or BH/BW>=T4, where T4 is a configured threshold (e.g., T4=1).

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a block based on a slice type (e.g., I-slice, B-slice, or P-slice) or picture type of the block as defined in the decoded information. For instance, the DIMD detection component 4112 may apply DIMD to the block only when the slice type of the block is an I-slice. In some other instances, the DIMD detection component 4112 may determine whether to apply DIMD to one or more temporal layers of the encoded bitstream 4120 when the decoded information indicates that hierarchical coding was employed during the encoding process.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on signaling. For instance, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on signaling in a sequence parameter set (SPS), picture parameter set (PPS), picture header, slice header, CTU, CU, and/or PU. Further, the signaling may correspond to a particular decoding unit (e.g., a block) or a plurality of decoding units.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on a DIMD indicator signalled as syntax element. Additionally, or alternatively, the syntax element may include a length of the IPM candidate set used to apply DIMD to the decoding unit. In some instances, the syntax element may be binarized using fix length coding, unary coding, truncated unary coding, Exp-Golomb coding, or coding a flag. In some other instances, the syntax element may be bypass coded. In yet still some other instances, the syntax element may be context coded. For instance, the syntax element may be based on decoded information. As described herein, the decoded information may be related to one or more attributes of a decoding unit, e.g., dimensions of a block, a function based on the dimensions of the block, a slice type of the block, picture type of the block, etc.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on the availability of one or more templates. For instance, the DIMD detection component 4112 may apply DIMD to a block based at least in part on the availability of templates and template-reference samples for deriving the IPM. In particular, the DIMD detection component 4112 may apply DIMD to a block based on one or more templates and template-reference samples associated with the block being available for deriving the IPM for the block. As used herein, in some aspects, a “template-reference sample” may refer to reconstructed samples used as a reference to derive predicted samples of a template.

As used herein, in some aspects, the “availability of a template” may refer to whether the template has been reconstructed, located inside the picture/subpicture/tile/slice, and/or located in the same video unit as the template or/and current block. As used herein, in some aspects, the “availability of a template-reference sample” may refer to whether a template-reference sample has been reconstructed, located inside the picture/subpicture/tile/slice, and/or located in the same video unit as the template and/or current block. In some aspects, the samples for a block may be considered unavailable when all of the templates and template-reference samples under consideration are unavailable or at least one of the templates and/or template-reference samples under consideration is unavailable.

In some examples, the DIMD detection component 4112 may determine whether to apply DIMD based on a relationship between the videos units including a current block, the plurality of templates associated with the current block, and the plurality of template-reference samples associated with the current block, respectively. Some examples of a video unit include PU, CU, VPDU, CTU, CTU row, CTU slice, CTU tile, or CTU/sub-picture. In some instances, the DIMD detection component 4112 may apply DIMD to a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are co-located within the same video unit.

In some other instances, the DIMD detection component 4112 may apply DIMD to a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are not co-located within the same video unit. Further, the DIMD component 4114 may perform DIMD using a default IPM when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the default IPM may include a DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, or diagonal top-left mode. In some other aspects, the default IPM may be derived from neighboring blocks of the current block. In yet still some other aspects, the default IPM may be derived from the decoded information. Additionally, or alternatively, the DIMD component 4114 may perform DIMD using a plurality of modified reference-template samples or a plurality of modified templates when the block, the plurality of templates (M2), and the plurality of template-reference samples (M1) are not co-located within the same video unit. In some aspects, the number of lines, rows, or columns (M1) of the reference-template samples to N1 and/or the number of lines, rows, or columns (M2) of the templates may be modified to N2 when the first video unit is different from the second video unit or/and the third video unit. In some examples, N1 is less than or equal to M1 (e.g., M1=4, N1=1 or M1=2, N1=1), and N2 is less than or equal to M2 (e.g., M2=4, N2=1 or M2=2, N2=1).

In some instances, the DIMD detection component 4112 may determine whether to apply DIMD to a decoding unit based on an intra coding tool. As an example, the DIMD detection component 4112 may determine to apply DIMD based on the absence of signaling including information associated with an application of an intra coding tool to the current block. Alternatively, the DIMD detection component 4112 may determine not to apply DIMD based on the presence of signaling including information associated with an application of an intra coding tool to the current block and/or the absence of signaling indicating the application of DIMD to the current block. Some examples of an intra coding tool include intra sub-partitions (ISP), multiple reference line (MRL), cross-component linear model (CCLM) prediction mode, matrix weighted intra prediction (MIP), and/or position dependent intra prediction combination (PDPC).

Further, in some aspects, a first syntax element may indicate the use of a derived IPM and a second syntax element may indicate the use of an intra coding tool. For example, a first syntax element may indicate whether a derived IPM is used and a second syntax element may indicate whether ISP is used. Further, in some aspects, if one of the syntax elements are determined using context coding, the context coded syntax element may be based on the other syntax element. For example, if the derived IPM is used with ISP and the first syntax element is context coded, the context of the first syntax element may be based on the second syntax element. Further, if the second syntax element is context coded, the context of the second syntax element may be based on the first syntax element. In some other examples, the syntax elements may not be based on each other.

As another example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, DIMD enabling component 4212, bitstream generating component 4214, and/or signaling component 4216 may be configured to or may comprise means for determining to apply decoder-side intra mode derivation to a unit of a bitstream.

For example, the determining at block 4302 may include determining to apply decoder-side intra mode derivation to a unit of a bitstream. In some aspects, a unit may include a block, picture, sub-picture, tile, slice, CTU, VPDU, CTU row, CU, or PU. Further, in some aspects, the DIMD enabling component 4212 may not enable DIMD for all of the blocks within the encoding unit. For example, the DIMD enabling component 4212 may enable DIMD for a first block within a CU and disable DIMD for a second block within the same CU.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on the dimensions of the block and/or a shape of the block of the plurality of pictures 4220. For instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width multiplied by the block height is larger than or equal to T1 (e.g., T1=16/64/256). In some other instances, the DIMD enabling component 4212 may enable DIMD for a block when the block width multiplied by the block height is less than or equal to T2 (such as T2=16/64/256/1024). In another instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width divided by the block height or the block height divided by block width is is less than or equal to T3 (such as T3=4/8). In yet another instance, the DIMD enabling component 4212 may enable DIMD for a block when the block width divided by the block height or the block height divided by block width is larger than or equal to T4 (such as T4=1).

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on a slice type or picture type of the block. For instance, the DIMD enabling component 4212 may enable DIMD for the block only when the slice type of the block is an I-slice. In some other instances, the DIMD enabling component 4212 may enable DIMD for one or more temporal layers when hierarchical coding is being employed by the encoding component 4210 to generate the encoded bitstream 4222.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on the availability of one or more templates. For instance, the DIMD enabling component 4212 may enable DIMD for the block based at least in part on the availability of templates and template-reference samples for deriving the IPM. In particular, DIMD enabling component 4212 may enable DIMD for the block based on one or more templates and/or one or more template-reference samples associated with a block being available for deriving the IPM for the block. In some aspects, the samples for a block may be considered unavailable when all of the templates and template-reference samples under consideration are unavailable or at least one of the templates and/or template-reference samples under consideration is unavailable.

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on a relationship between the videos units including a block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the block, respectively. In some instances, the DIMD enabling component 4212 may enable DIMD for a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are co-located within the same video unit.

In some other instances, the DIMD enabling component 4212 may enable DIMD for a block when the block, the plurality of templates associated with the block, and the plurality of template-reference samples associated with the plurality of templates are not co-located within the same video unit. Further, DIMD may be performed using a default IPM when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the default IPM may include a DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, or diagonal top-left mode. In some other aspects, the default IPM may be derived from neighboring blocks to the current block. Additionally, or alternatively, DIMD may be performed using a plurality of modified reference-template samples or a plurality of modified templates when the block, the plurality of templates, and the plurality of template-reference samples are not located within the same video unit. In some aspects, the number of lines, rows, or columns (M1) of the reference-template samples to N1 and/or the number of lines, rows, or columns (M2) of the templates may be modified to N2 when the first video unit is different from the second video unit or/and the third video unit. In some examples, N1 is less than or equal to M1 (e.g., M1=4, N1=1 or M1=2, N1=1), and N2 is less than or equal to M2 (e.g., M2=4, N2=1 or M2=2, N2=1).

In some examples, the DIMD enabling component 4212 may determine whether to enable DIMD based on an intra coding tool. For instance, the DIMD detection component 4112 may determine to disable DIMD for a block based on the use of an intra coding tool that cannot be used with a derived IPM, or enable DIMD for a block based on the use of an intra coding tool that may be used with a derived IPM. Some examples of an intra coding tool include ISP, MRL, CCLM prediction mode, MIP, and/or PDPC.

Referring to FIG. 45 , at block 4504, the method 4500 includes determining applicability of an intra coding tool based on the at least one IPM. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, and/or the DIMD component 4114 may be configured to or may comprise means for determining applicability of an intra coding tool based on the at least one IPM. As another example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, DIMD enabling component 4212, bitstream generating component 4214, and/or signaling component 4216 may be configured to or may comprise means for determining applicability of an intra coding tool based on the at least one IPM.

For example, the decoding component 4110, and/or the DIMD component 4114 may determine whether the IPM can be used with a particular intra coding tool (e.g., ISP, MRL, CCLM, MIP, or PDPC). In some instances, as described herein, a particular intra coding tool may be applicable, while in some other instances the particular coding tool may not be applicable. As another example, the encoding component 4210 and/or the DIMD enabling component 4212 may determine whether the IPM can be used with a particular intra coding tool (e.g., ISP, MRL, CCLM, MIP, or PDPC). In some instances, as described herein, a particular intra coding tool may be applicable, while in some other instances the particular coding tool may not be applicable.

Referring to FIG. 45 , at block 4506, the method 4500 includes performing the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool. For example, in an aspect, the computing device 4102, the processor 4104, the memory 4106, the decoding component 4110, and/or the DIMD component 4114 may be configured to or may comprise means for performing the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool. As another example, in an aspect, computing device 4202, processor 4204, memory 4206, encoding component 4210, DIMD enabling component 4212, bitstream generating component 4214, and/or signaling component 4216 may be configured to or may comprise means for performing the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool.

For example, a derived IPM may be employed as described herein with an intra coding tool. For example, the derived IPM may be used with ISP. In some instances, the derived IPM may be applied to one or more parts of ISP to derive the predicted samples of the parts. In another instance, an individual IPM may be derived for each part of ISP. In some aspects, when deriving an individual IPM for each part of ISP, the derivation of IPM for each part may be same as the derivation of IPM for the whole block.

In some examples, a first syntax element may indicate whether the derived IPM is used and a second syntax element may indicate whether ISP is used. When the derived IPM is used with ISP and the first syntax is context coded, the context of the first syntax may depend on the second syntax element. Alternatively, in some aspects, the context of the first syntax element cannot depend on the second syntax element. In another example, when the second syntax is context coded, the context may depend on the first syntax. Alternatively, in some aspects, the context of the second syntax elements cannot depend on the first syntax element. In yet still some other examples, the first syntax element and/or the second syntax element may be bypass coded.

In some other examples, when the derived IPM is used with ISP, the decoding component 4110 may apply one or more transforms to the current block. Some examples of transforms that may be applied to the block include MTS and/or LFNST. In some instances, when the derived intra mode is used with ISP, the decoding component 4110 may be limited to applying only one transform in MTS. For example, the decoding component 4110 may apply DCT X or DST Y may be applied, where X and Y are integers. As another example, the decoding component 4110 may apply LFNST with an index equal to Z, where Z is an integer. In some aspects, Z may be equal to 0.

Further, as another example, the derived IPM may be used with MRL. Further, in some aspects, when a derived IPM is used with MRL, application of MRL may be limited to a particular reference line. For instance, in some aspects, when a derived IPM is used with MRL, only the second or third reference line may be supported in MRL. In some examples, MRL may be used with DIMD similarly to ISP.

Further, as yet still another example, the derived IPM may be used with MIP. In some instances, the decoding component 4110 may implement an MIP derived from a plurality of templates, and the DIMD component 4114 may be configured to apply the MIP mode to the decoding unit (e.g., a block). In some aspects, the MIP mode as implemented by the decoding component 4110 may include a MIP mode index and/or MIP transposed flag. Alternatively, is some examples, MIP cannot be applied with DIMD.

In some examples, if the DIMD enabling component 4212 does not enable DIMD, the signaling component 4216 may not signal usage of DIMD for a particular encoding unit. For example, if a derived IPM cannot be used with a particular intra coding tool, then the signaling unit 4216 may not signal the usage of DIMD when the intra coding tool is applied to the current block. In addition, if a derived IPM cannot be used with a particular intra coding tool, then the signaling unit 4216 may not signal the usage of the intra coding tool when a derived IPM is applied to the current block.

In some examples, when a derived IPM is used with a particular intra coding tool, the signaling component 4216 may signal information corresponding to use of DIMD (e.g., information corresponding to the derived IPM) and information related to use of the particular intra coding tool. As an example, the signaling component may signal a first syntax element indicating that a derived IPM was used and a second syntax element indicating the use of an intra coding tool (e.g., ISP). Further, the signaling component 4216 may signal the information corresponding to the intra coding tool before or after information corresponding to the use of DIMD. For example, the signaling component 4216 may signal information related to a derived IPM (e.g., a DIMD flag/index) before or after information corresponding to MIP, ISP, and/or MRL (e.g., a MRL index) within the encoded bitstream 4222.

In some aspects, when application of DIMD is permitted with respect to blocks having a particular intra coding tool applied (e.g., MIP, MRL, ISP), the signaling component 4216 may not signal an indication of use of the DIMD. Alternatively, when application of DIMD is not permitted with respect to blocks having a particular intra coding tool applied, the signaling component 4216 may signal an indication of use of the DIMD. Furthermore, in some aspects, the DIMD detection component 4112 may detect or infer use of an intra coding tool and/or DIMD, and process the encoded bitstream 4120 using any of the processes applied at the computing device 4202.

While the foregoing disclosure discusses illustrative aspects and/or embodiments, it should be noted that various changes and modifications could be made herein without departing from the scope of the described aspects and/or embodiments as defined by the appended claims. Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise.

The previous description is provided to enable any person having ordinary skill in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other aspects. The claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, where reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to a person having ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module,” “mechanism,” “element,” “device,” and the like may not be a substitute for the word “means.”

As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.”

The following clauses describes some embodiments and techniques.

1. A method for video processing, comprising: determining, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit; and performing the conversion based on the determining.

2. The method of clause 1, wherein the current video unit includes a first color component and a second color component, and the IPM is derived from the first color component and applied to the second color component.

3. The method of clause 2, wherein an indication of an application of the IPM to the second color component is related to a syntax element presented in the bitstream.

4. The method of clause 2, wherein the first color component and the second color component are of a different color component type in RGB format or YCbCr format.

5. The method of clause 1, wherein the current video unit includes a chroma block and a corresponding luma block, and a chroma derived mode is applied to the chroma block based on the IPM being derived from luma component and/or the IPM being applied to the corresponding luma block.

6. The method of clause 1, wherein the current video unit includes a chroma block and a corresponding luma block, and a chroma derived mode is not applied to a chroma block of the bitstream in response to an application of the IPM to the corresponding luma block.

7. The method of clause 1, wherein a derivation of the at least one IPM is further based on IPM candidate set, and wherein a first IPM candidate set for a first color component is different from a second IPM candidate set for a second color component.

8. The method of clause 7, wherein a size of the first IPM candidate set is different from a size of the second IPM candidate set, or the size of the first IPM candidate set is same as the size of the second IPM candidate set but has at least one different IPM candidate different from candidates in the second IPM candidate set.

9. The method of clause 1, wherein the at least one IPM is applied to the current unit based at least in part on coded information, wherein the coded information includes one or more of: a dimension or a shape of the current video unit, a slice type of a slice related to the current video unit, a temporal layer, and a syntax element presented in the bitstream.

10. The method of clause 1, wherein the at least one IPM is derived further based on a plurality of IPMs corresponding to a plurality of previously-coded units.

11. The method of clause 10, wherein the plurality of previously-coded units are neighbouring units of the current video unit, and the at least one IPM is equal to a most used intra mode from the plurality of neighbouring units.

12. The method of clause 1, wherein the at least one IPM is derived further based on a gradient value of a neighbouring sample of a current video unit.

13. The method of clause 12, wherein the at least one IPM is derived from a direction having a largest amplitude.

14. The method of clause 12, wherein the at least one IPM is to set a default mode based on a first number of directions having amplitudes within a predefined range.

15. The method of clause 14, wherein the default mode is one of a DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, or diagonal top-left mode.

16. The method of clause 1, wherein the conversion includes encoding the current video unit into the bitstream.

17. The method of clause 1, wherein the conversion includes decoding the current video unit from the bitstream.

18. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit; and perform the conversion based on the determining.

19. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit; and generating the bitstream based on the determining.

20. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit; and perform the conversion based on the determining.

21. The method of clause 1, wherein the current video unit is in a first unit, and the prediction mode derivation tool is applied to a current block of the first unit based on a relationship between the first unit, a second unit including the template region, and a third unit including reference-template samples used to derive the prediction samples of the template region.

22. The method of clause 21, wherein the current video unit is a prediction unit (PU), coding unit (CU), video processing and distribution unit (VPDU), coding tree unit (CTU), CTU row, slice, tile, or sub-picture.

23. The method of clause 21, wherein the prediction mode derivation tool is applied to the current video unit based on the first unit, the second unit, and the third unit being the same unit.

24. The method of clause 21, wherein the prediction mode derivation tool is applied to the current video unit based on the first unit being different from the second unit or/and the third unit.

25. The method of clause 21, wherein the prediction mode derivation tool is not applied to the current video unit of the first unit based on the first unit being different from the second unit or/and the third unit.

26. The method of clause 21, wherein the prediction mode derivation tool is not applied to the current video unit of the first unit based on the third unit being different from the first unit and the second unit.

27. The method of clause 21, wherein the at least one IPM is set equal to a default IPM based on the first unit being different from the second unit or/and the third unit.

28. The method of clause 27, wherein the default IPM is a planar mode, a dc mode, a horizontal mode, a vertical mode, a diagonal top-right mode, a diagonal bottom-left mode, or a diagonal top-left mode.

29. The method of clause 27, wherein the default IPM is based on a plurality of neighbouring video units or decoded information of the current video unit.

30. The method of clause 21, wherein a number of lines, rows, or columns of the reference-template samples are modified based on the first unit being different from the second unit and/or the third unit.

31. The method of clause 21, wherein a number of lines, rows, or columns of the reference-template samples are reduced based on the first unit being different from the second unit and/or the third unit.

32. The method of clause 21, wherein a number of lines, rows, or columns of the reference-template samples is modified based on the second unit being different from the third unit.

33. The method of clause 21, wherein a number of lines, rows, or columns of the reference-template samples is reduced based on the second unit being different from the third unit.

34. The method of clause 21, wherein the prediction mode derivation tool is not applied to the current video unit based on an unavailability of the template region or an unavailability of the reference-template samples.

35. A method for video processing, comprising: determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; and performing a conversion based on the determining, wherein a syntax element is presented in the bitstream to indicate related information of the prediction mode derivation tool.

36. The method of clause 35, wherein the related information includes an application of DIMD or a length of an IPM candidate set used to derive the at least one IPM.

37. The method of clause 35, wherein the syntax element is binarized with fixed length coding, truncated unary coding, unary coding, EG coding, or coded as a flag.

38. The method of clause 35, wherein the syntax element is bypass coded.

39. The method of clause 35, wherein the syntax element is context coded.

40. The method of clause 39, wherein the context of the syntax element is based on coded information of the current block of the bitstream.

41. The method of clause 40, wherein the coded information corresponds to dimensions of the current block.

42. The method of clause 40, wherein a width of the current block (BW) and a height of the current block (BH) is included in the coded information, a first context is used when a product of the BW and the BH is less than or equal to a predefined number, and a second context is used when the product of the BW and the BH is greater than the predefined number.

43. The method of clause 40, wherein a width of the current block (BW) and a height of the current block (BH) is included in the coded information, a first context is used when a dividend of the BW and the BH is less than or equal to a predefined number, and a second context is used when the dividend of the BW and the BH is greater than the predefined number.

44. The method of clause 40, wherein the coded information corresponds to a slice type of the current block.

45. The method of clause 40, wherein the coded information corresponds to information from one or more neighbouring blocks of the current block.

46. The method of clause 45, wherein the one or more neighbouring blocks is a left block, an above block, a left-below block, a right-above block, or a left-above block.

47. The method of clause 45, wherein the coded information indicates whether the one or more neighbouring blocks are intra coded.

48. The method of clause 40, wherein the coded information indicates whether neighbouring blocks of the current block are the prediction mode derivation tool coded.

49. The method of clause 40, wherein the coded information indicates one or more other intra coding methods applied to the current block, wherein the other intra coding methods include intra sub-partitions, multiple reference line, and matrix-based intra prediction.

50. The method of clause 40, wherein the coded information corresponds to partition information of the current video block.

51. The method of clause 50, wherein the partition information corresponds to dual tree, single tree, local dual tree, or local single tree.

52. The method of clause 35, wherein the syntax element is presented in the bitstream based upon coded information corresponding to the current block.

53. The method of clause 52, wherein the coded information includes dimensions of the current block and/or a shape of the current block.

54. The method of clause 52, wherein a width of the current block (BW) of another block and a height of another block (BH) is included in the coded information, the syntax element is a first syntax element, and a second syntax element is not signalled for the another block when the coded information indicates that a product of the BW and the BH is less than or equal to a predefined number.

55. The method of clause 52, wherein a width of the current block (BW) of another block and a height of another block (BH) is included in the coded information, the syntax element is a first syntax element, and a second syntax element is not signalled for the another block when the coded information indicates that a product of the BW and the BH is greater than a predefined number.

56. The method of clause 52, wherein a width of the current block (BW) of another block and a height of another block (BH) is included in the coded information, the syntax element is a first syntax element, and a second syntax element is not signalled for the another block when the coded information indicates that a dividend of the BW and the BH is less than or equal to a predefined number.

57. The method of clause 52, wherein a width of the current block (BW) of another block and a height of another block (BH) is included in the coded information, the syntax element is a first syntax element, and a second syntax element is not signalled for the another block when the coded information indicates that a dividend of the BW and the BH is greater than a predefined number.

58. The method of clause 52, wherein the coded information include to slice type of the current block or a picture type of the current block.

59. The method of clause 52, wherein the coded information includes a prediction mode and/or an intra coding tool applied to the current block.

60. The method of clause 52, wherein the syntax element is not presented in the bitstream and is inferred to 1.

61. The method of clause 52, wherein the syntax element is not presented in the bitstream and is inferred to 0.

62. The method of clause 52, wherein the information is first information, and second information related to the prediction mode derivation tool is not presented in the bitstream based on an unavailability of the template region or an unavailability of the template-reference samples.

63. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, during a conversion between a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video unit, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current video unit based on cost calculations between reconstructed samples and prediction samples of a template region related the current video unit; and perform the conversion based on the determining.

64. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining during a conversion between a current block of the video and the bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; and performing the conversion based on the determining, wherein a syntax element is presented in the bitstream to indicate related information of the prediction mode derivation tool.

65. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; and perform a conversion based on the determining, wherein a syntax element is presented in the bitstream to indicate related information of the prediction mode derivation tool.

66. A method for video processing, comprising: determining during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; determining applicability of an intra coding tool based on the at least one IPM; and performing the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool.

67. The method of clause 66, wherein the at least one intra prediction mode is not applied to the current block based on application of the intra coding tool to the current block.

68. The method of clause 67, wherein information associated with the prediction mode derivation tool is not presented in the bitstream.

69. The method of clause 66, wherein information associated with the intra coding tool is not presented in the bitstream based on application of the prediction mode derivation tool to the current block.

70. The method of clause 66, wherein information associated with the intra coding tool is presented in the bitstream before information associated with the prediction mode derivation tool.

71. The method of clause 66, wherein information associated with the intra coding tool is presented in the bitstream after information associated with the prediction mode derivation tool.

72. The method of clause 66, wherein the intra coding tool includes at least one of intra sub-partitions (ISP), multiple reference line (MRL) intra prediction, cross-component linear model (CCLM), matrix weighted intra prediction (MIP), or position dependent intra prediction combination (PDPC).

73. The method of clause 66, wherein the intra coding tool is intra sub-partitions (ISP).

74. The method of clause 73, wherein the at least one IPM is applied to one or more parts of ISP to derive the predicted samples of the parts.

75. The method of clause 74, wherein the at least one IPM is derived for an individual part of ISP.

76. The method of clause 75, wherein the at least one IPM includes a first IPM derived for an individual part of ISP, and a second IPM derived for a whole block, and wherein the first IPM is the same as the second IPM.

77. The method of clause 76, wherein a first syntax element (SE) indicates whether the at least one IPM is used and a second syntax element (SE) indicates whether ISP is used.

78. The method of clause 77, wherein a context of the first SE depends on the second SE in response to ISP using the at least one IPM and the first SE being context coded.

79. The method of clause 77, wherein a context of the second SE depends on the first SE.

80. The method of clause 77, wherein a context of the first SE cannot depend on the second SE or a context of the second SE cannot depend on the first SE.

81. The method of clause 77, wherein the first SE or/and the second SE are bypass coded.

82. The method of clause 76, wherein one or more transforms is applied to the current block based on the at least one IPM being used with ISP.

83. The method of clause 82, wherein the one or more transforms include at least one of multiple transform selection (MTS) or low-frequency non-separable transform (LFNST).

84. The method of clause 82, wherein only an MTS transform is applied based on use of the at least one IPM for ISP.

85. The method of clause 82, wherein at least one of a discrete cosine transform or a discrete sine transform is applied as a transform.

86. The method of clause 82, wherein only low-frequency non-separable transform (LFNST) is applied with an integer value as an index.

87. The method of clause 86, wherein the index is equal to 0.

88. The method of clause 66, wherein the intra coding tool is multiple reference line (MRL).

89. The method of clause 88, wherein only a predefined reference line is supported and MRL index is not signalled.

90. The method of clause 89, wherein the predefined reference line is a second reference line or a third reference line.

91. The method of clause 88, wherein a prediction mode derivation tool flag or a prediction mode derivation tool index is presented in the bitstream before a MRL index.

92. The method of clause 88, wherein a prediction mode derivation tool flag or a prediction mode derivation tool index is presented in the bitstream after a MRL index.

93. The method of clause 66, wherein a matrix weighted intra prediction (MIP) mode is derived using the template region.

94. The method of clause 93, wherein a MIP mode index and/or a MIP transposed flag is derived using the template region.

95. The method of clause 66, wherein the prediction mode derivation tool is not applied to a block in which at least one of matrix weighted intra prediction (MIP), multiple reference line (MRL), or intra sub-partitions (ISP) is applied, an indication of usage of the prediction mode derivation tool is not presented in the bitstream, and the prediction mode derivation tool is disabled for the block.

96. The method of clause 66, wherein the intra coding tool includes at least one intra coding tool includes at least one of intra sub-partitions (ISP), multiple reference line (MRL) intra prediction, cross-component linear model (CCLM), matrix weighted intra prediction (MIP), or position dependent intra prediction combination (PDPC).

97. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; determine applicability of an intra coding tool based on the at least one IPM; and perform the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool.

98. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining during a conversion between a current block of the video and the bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; determining applicability of an intra coding tool based on the at least one IPM; and performing the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool.

99. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine during a conversion between a current block of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current block, wherein in the prediction mode derivation tool, at least one intra prediction mode (IPM) is derived for the current block based on cost calculations between reconstructed samples and prediction samples of a template region related the current block; determine applicability of an intra coding tool based on the at least one IPM; and perform the conversion based on the determining to apply the prediction mode derivation tool and/or the determining the applicability of the intra coding tool.

The detailed inventions below should be considered as examples to explain general concepts. These inventions should not be interpreted in a narrow way. Furthermore, these inventions can be combined in any manner. In this disclosure, the term DIMD represents a coding tool that derives intra prediction mode using previously decoded blocks. In aspects of this disclosure, the “conventional intra prediction mode (IPM) candidate set” is used to indicate the allowed IPMs for intra-coded blocks (e.g., the 35 modes in HEVC, the 67 modes in VVC), and a “conventional intra prediction mode” may refer to an IPM in the conventional IPM candidate set. In this disclosure, the “horizontal mode” refers to the intra prediction mode with mode number being equal to 18 in FIG. 6 . The “vertical mode” refers to the intra prediction mode with mode number being equal to 50 in FIG. 6 . The “diagonal top-right mode” refers to the intra prediction mode with mode number being equal to 65 in FIG. 6 . The “diagonal bottom-left mode” refers to the intra prediction mode with mode number being equal to 2 in FIG. 6 . The “diagonal top-left mode” refers to the intra prediction mode with mode number being equal to 34 in FIG. 6 . These intra prediction modes may also refer to the intra prediction modes having the same direction in HEVC.

In aspects of this disclosure, the “availability of the template” refers to whether the template has been reconstructed, or/and inside the picture/subpicture/tile/slice, or/and the template is in the same video unit as the template or/and current block. In aspects of this disclosure, the “template-reference samples” refers to the reconstructed samples used as the reference to derive the predicted samples of a template. In aspects of this disclosure, the “available template-reference samples” may refer to the template-reference samples have been reconstructed, or/and inside the picture/subpicture/tile/slice, or/and the template-reference samples are in the same video unit as the template or/and current block. In aspects of this disclosure, the “unavailable template-reference samples” may refer to the template-reference samples have not been reconstructed, or outside the picture/subpicture/tile/slice, or the template-reference samples are in the different video units from the template or/and current block. In this disclosure, the “the (derived) IPM is applied/used/enabled to a block” refers to the predictor of the block is generated using the (derived) IPM.

On usage of DIMD

-   -   1. Whether to and/or how to the derived IPM may depend on colour         component.         -   a. In one example, the IPM may be derived from a first             component and may be applied to a second component.             -   i. In one example, the first component may be same as                 the second component.                 -   1) Alternatively, the first component may be                     different from the second component.             -   ii. In one example, indications for the derived IPM                 applied to which colour component may be signalled with                 a syntax element.             -   iii. In one example, the first component may be Y in the                 YCbCr format, or G in RGB format.             -   iv. In one example, the first component may be Cb in the                 YCbCr format, or B in RGB format.             -   v. In one example, the first component may be Cr in the                 YCbCr format, or R in RGB format.             -   vi. In one example, the second component may be Y in the                 YCbCr format, or G in RGB format.             -   vii. In one example, the second component may be Cb in                 the YCbCr format, or B in RGB format.             -   viii. In one example, the second component may be Cr in                 the YCbCr format, or R in RGB format.         -   b. In one example, DM mode may be applied to a chroma block             when IPM is derived from luma component or/and the derived             IPM is applied to corresponding luma block of the chroma             block.             -   i. In one example, DM mode may be always applied to the                 chroma block when the derived IPM is applied to the                 corresponding luma block of the chroma block.             -   ii. Alternatively, DM mode may not be applied to the                 chroma block when the derived IPM is applied to                 corresponding luma block of the chroma block.         -   c. In one example, the given IPM candidate sets used to             derive the IPM for different colour components may be             different.             -   i. For example, the size of the given IPM candidate set                 used to derive a IPM for a luma block may be larger than                 or less than that of the given IPM candidate set used                 for a chroma block.             -   ii. In one example, the size of the given IPM candidate                 set used to derive a IPM for a luma block may be equal                 to that of the given IPM candidate set used for a chroma                 block.     -   2. Whether to and/or how to apply the derived IPM may be         dependent on the decoded information.         -   a. For example, whether to and/or how to apply the derived             IPM may depend on block dimensions/block shape. Denote block             width and block height as BW and BH.         -   b. In one example, the derived IPM may not be applied for             all the blocks in a video unit.             -   i. In one example, the video unit may refer to                 picture/sub-picture/tile/slice/CTU/VPDU/CTU row/CU/PU.         -   c. In one example, whether to or how to apply the derived             IPM may depend on a function of BW or/and BH.             -   i. In one example, the function may be related to block                 width or/and block height.             -   ii. In one example, the derived IPM may be applied to a                 block only when BW×BH is larger than or equal to T1                 (such as T1=16/64/256).             -   iii. In one example, the derived IPM may be applied to a                 block only when BW×BH is less than or equal to T2 (such                 as T2=16/64/256/1024).             -   iv. In one example, the derived IPM may be applied to a                 block only when BW/BH or BH/BW is less than or equal to                 T3 (such as T3=4/8).             -   v. In one example, the derived IPM may be applied to a                 block only when BW/BH or BH/BW is larger than or equal                 to T4 (such as T4=1).         -   d. In one example, whether the derived IPM can be applied to             a block may be dependent on slice type.             -   i. In one example, the derived IPM can only be applied                 to I slice.             -   ii. In one example, the derived IPM can only be applied                 to P or/and B slice.             -   iii. In one example, the derived IPM can only be to                 apply to one or more temporal layers when hierarchical                 coding is used (such as only applied to the lowest                 temporal layer).         -   e. Alternatively, whether the derived IPM can be applied             and/or how to apply the derived IPM for a video unit may be             signalled to the decoder such as in SPS/PPS/picture             header/slice header/CTU/CU/PU.     -   3. In one example, the derived IPM may be derived using the IPMs         of previously coded blocks.         -   a. In one example, it may be derived using the IPMs of             neighbouring blocks.             -   i. In one example, the derived IPM may be set equal to                 the most used intra mode from the neighbouring blocks.         -   b. In one example, it may be derived using the IPMs of             previously coded blocks in a region.     -   4. In one example, the derived IPM may be derived by calculating         the gradients of the neighbouring samples.         -   a. In one example, the derived IPM may be derived from a             direction with the largest amplitude.         -   b. In one example, the derived IPM may be set a default mode             when the first X directions have similar amplitudes.             -   i. In one example, the default mode may be DC, or/and                 Planar, or/and horizontal degree mode, or/and vertical                 degree mode, or/and diagonal top-right degree mode,                 or/and diagonal bottom-left mode, or/and diagonal                 top-left mode.     -   5. In one example, above methods on usage of the derived IPM may         be applied to the methods on derivation of multiple IPMs         disclosed in bullet 8.

Signalling of DIMD

-   -   6. In one example, information related to DIMD (e.g., whether         DIMD is applied or the length of the given IPM candidate set)         may be signalled as a syntax element.         -   a. In one example, the syntax element may be binarized with             fixed length coding, or truncated unary coding, or unary             coding, or EG coding, or coded a flag.         -   b. In one example, the syntax element may be bypass coded.         -   c. Alternatively, the syntax element may be context coded.             -   i. The context may depend on decoded information.                 -   1) In one example, the decoded information may refer                     to block width or/and block height, denoted as BW                     and BH.                 -    a) In one example, different contexts may be used                     when BW×BH≤T₁ and BW×BH>T₁.                 -    b) In one example, different contexts may be used                     when BW/BH≤T₂ and BW/BH>T2.                 -   2) In one example, the decoded information may refer                     to a slice type.                 -   3) In one example, the decoded information may refer                     to that information from one or more neighbouring                     blocks.                 -    a) In one example, the neighbouring blocks may                     refer to left, or/and above, or/and left-below,                     or/and right-above, or/and left-above block.                 -    b) In one example, the decoded information may                     refer to whether the neighbouring blocks are intra                     coded.                 -    c) In one example, the decoded information may                     refer to whether the neighbouring blocks are DIMD                     coded.                 -   4) In one example, the decoded information may refer                     to the methods applied to current block (e.g.,                     ISP/MRL/MIP).                 -   5) In one example, the decoded information may refer                     to the partition information (e.g., dual or single                     tree, local dual tree or single tree).         -   d. Whether the syntax element is signalled may depend on             decoded information.             -   i. In one example, the decoded information may refer to                 block dimensions or/and block shape. Denote block width                 and block height as BW and BH.                 -   a) In one example, the syntax element may be not                     signalled when BW×BH≤T₁.                 -   b) Alternatively, the syntax element may be not                     signalled when BW×BH>T₁.                 -   c) In one example, the syntax element may be not                     signalled when BW/BH≤T₂.                 -   d) Alternatively, the syntax element may be not                     signalled when BW/BH>T₂.             -   ii. In one example, the decoded information may refer to                 slice/picture types.             -   iii. In one example, the decoded information may refer                 to prediction mode (e.g., IBC, palette mode) and/or                 intra coding tools (e.g., MRL, ISP, MIP).             -   iv. In one example, when the syntax element is not                 signalled, it may be inferred to 1.                 -   1) Alternatively, the syntax element may be inferred                     to 0.         -   e. In one example, when none of templates are unavailable to             derive the IPM, DIMD cannot be applied to the block.             -   i. In one example, the information related to DIMD is                 not signalled when none of templates are unavailable.             -   ii. In one example, when the template-reference samples                 are unavailable to derive the IPM, DIMD cannot be                 applied to the block.             -   iii. In one example, the information related to DIMD is                 not signalled when the template-reference samples are                 unavailable.             -   iv. “samples are unavailable” may refer to all samples                 under consideration are unavailable or at least one of                 the samples under consideration is unavailable.     -   7. During the IPM derivation, suppose the current block is in a         first video unit, the template is in a second video unit, and         the template-reference samples of the template are in a third         unit. Whether DIMD can be applied to current block and/or the         IPM derivation may depend on the relationship of the first video         unit, or/and the second video unit, or/and the third video unit.         -   a. In one example, the video unit may refer to             PU/CU/VPDU/CTU/CTU row/slice/tile/sub-picture.         -   b. In one example, DIMD can be applied to the current block             when the first video unit, the second video unit, and the             third video unit are the same video unit.         -   c. In one example, DIMD cannot be applied to current block             when the first video unit is different from the second video             unit or/and the third video unit.             -   i. Alternatively, DIMD still can be applied to current                 block when the first video unit is different from the                 second video unit or/and the third video unit.                 -   1) In one example, the derived IPM may be set equal                     to a default IPM when the first video unit is                     different from the second video unit or/and the                     third video unit.                 -    a) In one example, the default IPM may refer to                     Planar/DC/horizontal mode/vertical mode/diagonal                     top-right mode/diagonal bottom-left mode/diagonal                     top-left mode.                 -    b) In one example, the default IPM may be derived                     from neighbouring blocks.                 -    c) In one example, the default IPM may be derived                     from the decoded information.             -   ii. In one example, DIMD cannot be applied to current                 block when the first video unit and the second video                 unit are the same, but different from the third video                 unit.         -   d. In one example, the number of lines/rows/columns (denoted             as M1) of the reference-template samples may be modified to             N1 when the first video unit is different from the second             video unit or/and the third video unit.             -   i. In one example, N1 is less than or equal to M1, such                 as M1=4, N1=1 or M1=2, N1=1.             -   ii. In one example, the number of sample                 lines/rows/columns (denoted as M2) of the template may                 be modified to N2 when the second video unit is                 different from the third video unit.                 -   1) In one example, N2 is less than or equal to M2,                     such as M2=4, N2=1 or M2=2, N2=1.

Interaction Between DIMD with Other Tools

-   -   8. The derived IPM may also be used with a specific intra coding         tool.         -   a. Alternatively, the derived IPM cannot be used with an             intra coding tool.             -   i. E.g., if the derived IPM cannot be used with a                 specific intra coding tool X, then the information                 related to DIMD (e.g., whether DIMD is applied) may not                 be signalled if tool X is applied to current block.             -   ii. E.g., if the derived IPM cannot used with a specific                 intra coding tool X, then the information related to X                 (e.g., whether tool X is applied) may not be signalled                 if the derived IPM is applied to current block.             -   iii. The information related to the derived IPM may be                 signalled before the information related to tool X.                 -   1) In one example, the information related to the                     derived IPM may be signalled before the information                     of MIP, or/and ISP, or/and MRL.             -   iv. The information related to the derived IPM may be                 signalled after the information related to tool X.                 -   1) In one example, the information related to the                     derived IPM may be signalled after the information                     of MIP, or/and ISP, or/and MRL.         -   b. In one example, the specific intra coding tool may refer             to ISP, or/and MRL, or/and CCLM, or/and MIP, or/and PDPC.         -   c. In one example, the derived IPM may be used with ISP.             -   i. Alternatively, the derived IPM cannot be used with                 ISP.             -   ii. In one example, the derived IPM may be applied to                 one or more parts of ISP to derive the predicted samples                 of the parts.             -   iii. In one example, an individual IPM may be derived                 for each part of ISP.                 -   1) In one example, when deriving individual IPM for                     each part of ISP, the derivation of IPM for each                     part may be same as the derivation of IPM for the                     whole block.             -   iv. In one example, a first syntax element (SE)                 indicates whether the derived IPM is used and a second                 syntax element (SE) indicates whether ISP is used. When                 the derived IPM is used with ISP and the first SE is                 context coded, the context of the first SE may depend on                 the second SE.                 -   1) Alternatively, the context of the first SE cannot                     depend on the second SE.                 -   2) In one example, when the second SE is context                     coded, the context may depend on the first SE.                 -    a) Alternatively, the context of the second SE                     cannot depend on the first SE.                 -   3) In one example, the first SE or/and the second SE                     may be bypass coded.             -   v. In one example, when the derived IPM is used with                 ISP, one or more transforms may be applied to current                 block.                 -   1) In one example, the transform may refer to MTS,                     or/and LFNST, or one or more of MTS and LFNST.                 -   2) In one example, when the derived intra mode is                     used with ISP, only one kind of transform in MTS may                     be applied.                 -    b) In one example, DCT X/DST Y or may be applied,                     where X and Y are integers.                 -    c) In one example, only LFNST with index equal to Z                     may be applied, where Z is an integer.                 -    i. In one example, Z is equal to 0.         -   d. In one example, the derived IPM may be used with MRL.             -   i. Alternatively, the derived IPM cannot be used with                 MRL.             -   ii. In one example, the disclosed methods for DIMD                 harmonized with ISP may also be used for MRL.             -   iii. In one example, when the derived IPM is used with                 MRL, only a certain reference line may be supported in                 MRL and there is no need to signal the MRL index.                 -   1) In one example, when the derived IPM is used with                     MRL, only the second or third reference line may be                     supported.             -   iv. In one example, when the derived IPM is used with                 MRL, the DIMD flag/index may be signalled before the MRL                 index.                 -   2) Alternatively, the DIMD flag/index may be                     signalled after the MRL index.         -   e. In one example, the disclosed DIMD method above may be             applied with MIP.             -   i. In one example, a MIP mode may be derived using the                 templates and applied to current block.                 -   3) In one example, the MIP mode may consist of a MIP                     mode index or/and MIP transposed flag.             -   ii. Alternatively, above DIMD method cannot be applied                 with MIP.         -   f. In above example, when DIMD is not disallowed to be             applied to blocks with certain modes (e.g., MIP, MRL, ISP),             indication of usage of the DIMD is not signalled.             -   i. Alternatively, when DIMD is not allowed to be applied                 to blocks with certain modes (e.g., MIP, MRL, ISP),                 indication of usage of the DIMD is still signalled                 (e.g., conditionally signalled), but shall be                 constrained that DIMD is disabled for the block. 

What is claimed is:
 1. A method for video processing, comprising: determining, during a conversion between a current video block of a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video block; and performing the conversion based on the determining; wherein in the prediction mode derivation tool, an intra prediction mode (IPM) candidate set comprising at least one IPM is constructed, a derived IPM is derived from the IPM candidate set for the current video block based on cost calculations between reconstructed samples and prediction samples of a template region related the current video block, and one or more syntax elements specifying the derived IPM is omitted from the bitstream; and wherein the template region related to the current video block locates outside the current video block.
 2. The method of claim 1, wherein the current video unit includes a first color component and a second color component which is the current video block, and the derived IPM is derived from the first color component.
 3. The method of claim 2, wherein an indication of an application of the derived IPM to the second color component is related to a syntax element presented in the bitstream.
 4. The method of claim 2, wherein the first color component and the second color component are of a different color component type in RGB format or YCbCr format.
 5. The method of claim 1, wherein the current video unit includes a chroma block and a corresponding luma block which is the current video block, and a chroma derived mode is applied to the chroma block based on the derived IPM being derived from luma component and/or the derived IPM being applied to the corresponding luma block.
 6. The method of claim 1, wherein the current video unit includes a chroma block and a corresponding luma block which is the current video block, and a chroma derived mode is not applied to the chroma block in response to an application of the derived IPM to the corresponding luma block.
 7. The method of claim 1, wherein the current video unit includes a first color component which is the current video block and a second color component, and wherein the IPM candidate set for the first color component is different from a second IPM candidate set for the second color component.
 8. The method of claim 7, wherein a size of the IPM candidate set is different from a size of the second IPM candidate set, or the size of the IPM candidate set is a same size as the size of the second IPM candidate set but has at least one different IPM candidate different from candidates in the second IPM candidate set.
 9. The method of claim 1, wherein the derived IPM is applied to the current video block based at least in part on coded information, wherein the coded information includes one or more of: a dimension or a shape of the current video block, a slice type of a slice related to the current video block, a temporal layer, and a syntax element presented in the bitstream.
 10. The method of claim 1, wherein the derived IPM is derived further based on a plurality of IPMs corresponding to a plurality of previously-coded blocks.
 11. The method of claim 10, wherein the plurality of previously-coded blocks are neighbouring blocks of the current video block, and the derived IPM is equal to a most used intra mode from the neighbouring blocks.
 12. The method of claim 1, wherein the derived IPM is derived further based on a gradient value of a neighbouring sample of the current video block.
 13. The method of claim 12, wherein the derived IPM is derived from a direction having a largest amplitude.
 14. The method of claim 12, wherein the derived at least one IPM is to set a default mode based on a first number of directions having amplitudes within a predefined range.
 15. The method of claim 14, wherein the default mode is one of a DC mode, planar mode, horizontal degree mode, vertical degree mode, diagonal top-right degree mode, diagonal bottom-left mode, or diagonal top-left mode.
 16. The method of claim 1, wherein the conversion includes encoding the current video block into the bitstream.
 17. The method of claim 1, wherein the conversion includes decoding the current video block from the bitstream.
 18. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, during a conversion between a current video block of a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video block; and perform the conversion based on the determining; wherein in the prediction mode derivation tool, an intra prediction mode (IPM) candidate set comprising at least one IPM is constructed, a derived IPM is derived from the IPM candidate set for the current video block based on cost calculations between reconstructed samples and prediction samples of a template region related the current video block, and one or more syntax elements specifying the derived IPM is omitted from the bitstream; and wherein the template region related to the current video block locates outside the current video block.
 19. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining, during a conversion between a current video block of a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video block; and generating the bitstream based on the determining; wherein in the prediction mode derivation tool, an intra prediction mode (IPM) candidate set comprising at least IPM is constructed, a derived IPM is derived from the IPM candidate set for the current video block based on cost calculations between reconstructed samples and prediction samples of a template region related the current video block, and one or more syntax elements specifying the derived IPM is omitted from the bitstream; and wherein the template region related to the current video block locates outside the current video block.
 20. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, during a conversion between a current video block of a current video unit of a video and a bitstream of the video, to apply a prediction mode derivation tool to the current video block; and perform the conversion based on the determining; wherein in the prediction mode derivation tool, an IPM candidate set comprising at least one intra prediction mode (IPM) is constructed, an IPM is derived from the IPM candidate set for the current video block based on cost calculations between reconstructed samples and prediction samples of a template region related the current video block, and one or more syntax elements specifying the derived IPM is omitted from the bitstream; and wherein the template region related to the current video block locates outside the current video block. 